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University of Calgary
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Graduate Studies The Vault: Electronic Theses and Dissertations
2013-01-25
Physiology and Molecular Characterization of
Microbial Communities in Oil Sands Tailings Ponds
Ramos Padron, Esther
Ramos Padron, E. (2013). Physiology and Molecular Characterization of Microbial Communities in
Oil Sands Tailings Ponds (Unpublished doctoral thesis). University of Calgary, Calgary, AB.
doi:10.11575/PRISM/27356
http://hdl.handle.net/11023/494
doctoral thesis
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UNIVERSITY OF CALGARY
“Physiology and Molecular Characterization of Microbial Communities
in Oil Sands Tailings Ponds”
by
Esther Ramos Padrón
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATE STUDIES
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF BIOLOGICAL SCIENCES
CALGARY, ALBERTA
JANUARY, 2013
© Esther Ramos-Padrón 2013
ii
Abstract
In northern Alberta, mining operations to obtain bitumen from the oil sands generates
large volumes of tailings. These are a mixture of sand, clay, water, organic solvents and
residual bitumen that are deposited into old open pits, creating tailings ponds, where they are
allowed to settle with the final goal of land reclamation. To speed up the sedimentation
process, the addition of gypsum (CaSO4 ∙ 2H2O) is currently a management approach used
bysome companies. This creates a deep watery mud line with very low oxygen permeability
and enough sulfate to support the growth of anaerobic microbial communities. In this thesis
work, the microbial physiology and communities associated with oil sands tailings ponds were
assessed. Chemical, physiological, and molecular biology approaches were used to determine
the key microbial processes (methanogenesis, sulfate reduction/oxidation), identify key
substrates, and determine the dominant microbial community members in the anaerobic and
aerobic zones of tailings ponds. Microbial community analysis showed that in the anaerobic
zone of tailings, the sulfate-reducing/disproportionating bacterium Desulfocapsa. and the
sulfide oxidizer/iron reducer Thiobacillus sp. are among the most prevalent organisms when
sulfate is present. After sulfate is depleted, methanogenic Archaea become predominantly
active and Methanosaeta and Methanolinea in association with Syntrophus dominate in the
ponds, presumably interacting to biodegrade the available organic compounds. The residual
naphtha components that constitute part of the tailings composition are the preferred electron
donors in anaerobic zones (in comparison to naphthenic acids) based on enrichment culture
studies. In naphtha-amended laboratory cultures, a variety of methanogens in association with
Thauera sp. and Desulfocapsa sp. became enriched as the dominant organisms. Overall,
microbial community composition as a function of depth in tailings ponds paralleled key
iii
microbial processes that were measured (sulfate reduction and methanogenesis). In the aerobic
surface water, other microbes with known metabolic capabilities to degrade hydrocarbon-
derived compounds such as naphthenic acids were found. The results of this work also showed
that operational changes to tailings ponds shift the microbial community structure and
functions. For example, pond closure resulted in a shift from a predominantly methanogenic
and sulfate-reducing environment to one dominated by putative hydrocarbon degraders,
indicating a positive management outcome in microbial activity associated with pond closure.
iv
Acknowledgements
I would like to deeply thank my supervisor Dr. Lisa Gieg for accepting me as her first
PhD student. Thanks for sharing your knowledge and for the confidence in me. Thanks also
for your kindness, support and guidance during these years. It was really a pleasure working
with you.
A huge gratitude to my co-supervisor Dr. Gerrit Voordouw for accepting me in his
research group and for sharing his vast knowledge in the field of petroleum microbiology.
Thanks for teaching me how to design experiments in the simplest way to get the greatest
information out, and to better interconnect what we do in the lab to the industrial field.
I would also like to thank Dr. Joseph Fournier and Dr. Dipo Omotoso from Suncor
Energy Inc. for supplying all the tailings samples and for all the information regarding the
tailings ponds operations. Also, many thanks to Lindsay Clothier and Carolina Berdugo for
help with natural NA extraction and Kingsley Nze for help with some time course
experiments.
Thank you also to my committee members Dr. Michael Hynes and Dr. Alex de Visscher
for your support and advice on my research.
Thanks to all the members of the Gieg and Voordouw labs for sharing your knowledge
and for your support. Especially, thanks to Dr. Akhil Agrawal for your guidance and help in
the qPCR experiments. Also many thanks to my friends Sylvain Bordenave, Jane Fowler,
Shawna Johnston and Carolina Berdugo for their support in the lab and in my personal life.
v
I would also like to thank my mom, although far away, for her unconditional love and
support during these difficult years of my life. Thanks for the daily phone calls sharing your
wise and always certain advice when I most needed it.
Last but not least, thanks to my children Fabian and Javier, to whom this thesis is
dedicated, for their love and patience for not having an available mom every time they needed
me.
This work was supported in part by an NSERC Industrial Research Chair Award to
Gerrit Voordouw, which was also supported by Aramco Services, Baker Hughes Incorporated,
BP, Intertek-CML, the Computer Modelling Group Limited, ConocoPhillips Company, Shell
Canada Limited, Suncor Energy, Yara International ASA and YPF SA as well as by Alberta
Innovates-Energy and Environment Solutions. This work was also supported by funding to
Gerrit Voordouw and Lisa Gieg from Genome Canada, Genome Alberta, the Government of
Alberta and Genome BC.
vi
Dedication
To my children Fabian and Javier,
vii
Table of Contents
Abstract ................................................................................................................................ ii Acknowledgements ............................................................................................................ iv
Table of Contents .............................................................................................................. vii List of Tables ...................................................................................................................... xi List of Figures and Illustrations ........................................................................................ xiii List of Symbols, Abbreviations and Nomenclature ......................................................... xvi
CHAPTER ONE: LITERATURE REVIEW ...................................................................... 1
1.1 Oil sands tailings pond formation.............................................................................. 1 1.1.1 Surface mining for bitumen extraction ............................................................. 1
1.1.2 Tailings pond composition ................................................................................ 6 1.1.3 Tailings pond management and environmental concerns ............................... 10
1.2 Microbiology of tailings ponds ............................................................................... 13 1.2.1 Tailings ponds: a niche for microbial activity................................................. 13
1.2.1.1 Sulfate-reducing bacteria (SRB) and methanogens ............................... 15 1.2.1.2 Iron reducing bacteria (IRB) ................................................................. 17
1.2.1.3 Nitrate reducing bacteria (NRB) ........................................................... 20 1.2.1.4 Aerobic microorganisms in tailings ponds ............................................ 20
1.2.2 Sources of carbon for organisms living in tailings ponds ............................... 23
1.2.3 Molecular biology techniques for unveiling microbes in tailings ponds ........ 27
CHAPTER TWO: HYPOTHESIS AND OBJECTIVES .................................................. 30
CHAPTER THREE: METHODS AND MATERIALS .................................................... 32 3.1 Sampling and origin of oil sands tailings samples .................................................. 32
3.2 Chemical techniques ................................................................................................ 35 3.2.1 Dissolved hydrogen sulfide concentrations in tailings .................................... 35
3.2.1.1 Preparation of reagents .......................................................................... 35 3.2.1.2 Assay procedure .................................................................................... 35
3.2.2 Dissolved hydrogen sulfide assay method for SOB experiments ................... 36
3.2.2.1 Preparation of reagents .......................................................................... 36 3.2.2.2 Assay procedure .................................................................................... 36
3.2.3 Anion concentrations (nitrate, sulfate, and acetate) concentrations by HPLC 37 3.2.4 Water content .................................................................................................. 37
3.3 Microbial activity measuremets .............................................................................. 38
3.3.1 Sulfate reduction rates (SRR).......................................................................... 38
3.3.1.1 Preparation of reagents .......................................................................... 38 3.3.1.2 SRR technique ....................................................................................... 39
3.3.2 Methanogenesis rates ...................................................................................... 42 3.3.2.1 Sample preparation ................................................................................ 42 3.3.2.2 Methane measurements by gas chromatography ................................... 42
3.4 Microbial community composition ......................................................................... 43 3.4.1 DNA Extraction .............................................................................................. 43 3.4.2 16S r DNA Pyrosequencing ............................................................................ 43
3.4.3 Analysis of pyrosequencing data .................................................................... 45
viii
3.5 Microbial laboratory enrichments ........................................................................... 47 3.5.1 Incubation Media ............................................................................................ 49 3.5.2 Aerobic enrichments on naphthenic acids ....................................................... 49 3.5.3 Aerobic medium for sulfide oxidation assays ................................................. 50
3.5.4 Anaerobic enrichments .................................................................................... 50
CHAPTER FOUR: MICROBIAL PHYSIOLOGY AND COMMUNITIES IN OIL
SANDS TAILINGS PONDS ................................................................................... 55 4.1 Introduction ............................................................................................................. 55 4.2 Methods in brief ...................................................................................................... 58
4.2.1 Pond 6 (active pond) ....................................................................................... 58 4.2.2 Pond 5 (inactive pond) .................................................................................... 58
4.3 Pond 6, an active tailings pond ................................................................................ 59 4.3.1 Results ............................................................................................................. 61
4.3.1.1 Microbial community composition in pond 6 ....................................... 61 4.3.1.2 Relationship between pond 6 samples ................................................... 67
4.3.1.3 Microbial activity and chemistry of the pond ........................................ 70 4.4 Effect of pond closure: Pond 5, an inactive pond. ................................................... 74
4.4.1 Results ............................................................................................................. 77 4.4.1.1 Microbial community composition before and after pond 5 closure .... 77 4.4.1.2 Microbial relationship between the two sampling periods (before and
after pond closure) .................................................................................. 81 4.4.1.3 Sulfate-reducing and methanogenic activity in pond 5 before and after
closure ..................................................................................................... 84
4.5 Discussion................................................................................................................ 87
4.5.1 Physiological and chemical characterization of an active pond ...................... 87 4.5.2 Effect of pond closure ..................................................................................... 96
4.5.3 A comparison between active and inactive ponds ........................................ 100
CHAPTER FIVE: MICROBIOLOGY AT THE SURFACE OF TAILINGS PONDS .. 103 5.1 Introduction ........................................................................................................... 103
5.2 Methods ................................................................................................................. 105 5.2.1 Sulfide oxidation experiments ....................................................................... 105
5.2.2 DNA extraction and 454 pyrosequencing from tailings surface waters ....... 105 5.2.3 Isolation and identification of naphthenic acid-degrading bacterial isolates 106
5.2.4 NA biodegradation time course experiments ................................................ 106
5.3 Results ................................................................................................................... 108
5.3.1 Potential for sulfide oxidation at the surface of tailings pond ...................... 108 5.3.2 Microbial community composition of surface waters ................................... 110 5.3.3 Biodegradation experiments with NA isolates .............................................. 113 5.3.4 Naphthenic acid metabolite analysis ............................................................. 116
5.4 Discussion.............................................................................................................. 121
CHAPTER SIX: TARGETING SPECIFIC MICROBIAL FUNCTIONS IN OIL SANDS
TAILINGS PONDS BY QUANTITATIVE PCR. ................................................. 125 6.1 Introduction ........................................................................................................... 125
6.2 Methods ................................................................................................................. 126
ix
6.2.1 DNA extraction and selection of functional genes ....................................... 126 6.2.2 Primer design ................................................................................................ 128 6.2.3 Primer optimization, cloning, and qPCR assay ............................................. 130
6.2.3.1 Primer optimization ............................................................................. 130
6.2.3.2 TOPO TA cloning ............................................................................... 130 6.2.3.3 Quantitative PCR assay ....................................................................... 131
6.3 Results ................................................................................................................... 133 6.3.1 Functional gene primers selected and qPCR ................................................. 133 6.3.2 Correlation of functional genes with microbial activity and chemistry
composition as a function of depth in the tailings samples. .......................... 138 6.4 Discussion.............................................................................................................. 143
CHAPTER SEVEN: THE EFFECTS OF SUBSTRATES AND ALTERNATE
ELECTRON ACCEPTORS ON ANAEROBIC MICROBIAL COMMUNITES IN
OIL SANDS TAILINGS PONDS .......................................................................... 150 7.1 Introduction ........................................................................................................... 150
7.2 Methods ....................................................................................................... Esther151 7.2.1 Anaerobic enrichment to determine the effects of carbon sources for sulfate
reduction and methanogenesis in tailings ponds. .......................................... 151 7.2.2 Nitrate as an alternate electron acceptor in the presence of naphtha ............ 156
7.3 Results ................................................................................................................... 158
7.3.1 Methane and sulfate in carbon source enrichments experiments .................. 158 7.3.2 Microbial community when different carbon sources are available in tailings
....................................................................................................................... 163
7.3.3 Methane inhibition by nitrate ........................................................................ 166
7.3.4 Microbial community composition when nitrate is available ....................... 170 7.4 Discussion.............................................................................................................. 172
7.4.1 Naphtha vs. natural NAs vs. bitumen as electron donors for anaerobes in
tailings ponds ................................................................................................. 172 7.4.2 Nitrate as an alternate electron acceptor in tailings ponds ............................ 179
CHAPTER EIGHT: CONCLUSIONS ............................................................................ 185
REFERENCES ................................................................................................................ 192
APPENDIX ONE: LIST OF PRIMERS USED FOR 16 S RRNA GENE
AMPLIFICATION ................................................................................................. 207
APPENDIX TWO: MICROBIAL RANK IDENTIFIED IN POND 6 ........................... 208
APPENDIX THREE: MICROBIAL RANK IDENTIFIED IN POND 5 ....................... 211
APPENDIX FOUR: NAPHTHENIC ACID ISOLATES DNA SEQUENCES .............. 213
APPENDIX FIVE: DIVERSITY INDEXES FOR POND 6........................................... 214
APPENDIX SIX: RAREFACTION CURVE OF ALL POND 6 SAMPLES ................ 215
x
APPENDIX SEVEN: DIVERSITY INDEXES FOR POND 5 ...................................... 216
APPENDIX EIGHT: RAREFACTION CURVE POND 5. ............................................ 217
APPENDIX NINE: DIVERSITY INDEXES FOR SURFACE WATER SAMPLES ... 218
APPENDIX TEN: RAREFACTION CURVES FOR SURFACE WATER SAMPLES 219
APPENDIX ELEVEN: SULFUR METABOLISM IN TAILINGS FROM POND 6 2008
AND 2010. OBTAINED FROM METAGENOMIC ANALYSIS BY KEGG
(HTTP://WWW.GENOME.JP/KEGG/) ................................................................. 220
APPENDIX TWELVE: IRON CONCENTRATION IN OIL SANDS TAILINGS PONDS
................................................................................................................................ 221
xi
List of Tables
Table 3-1 Suncor Pond 5 sample information .......................................................................... 34
Table 3-2 Suncor Pond 6 sample information .......................................................................... 34
Table 3-3 General overview of all tailings samples used for microbial community analysis
by 454 pyrosequencing and for the various experiments described in this thesis. ........... 48
Table 3-4 Modified Bushnell - Haas salt (MBH) medium composition. ................................. 52
Table 3-5 LB (lysogenic broth) medium .................................................................................. 52
Table 3-6 CSB-A medium composition. .................................................................................. 52
Table 3-7 General anaerobic medium composition .................................................................. 53
Table 3-8 Pfennig solutions ...................................................................................................... 53
Table 3-9 Wolin trace metal solution ....................................................................................... 54
Table 3-10 Balch vitamin solution ........................................................................................... 54
Table 4-1 Average SRR, methanogenesis rates, and putative methane evolution prevented
in various samples collected over time in pond 6. ............................................................ 73
Table 5-1 Surface tailings pond water isolates obtained and grown on model naphthenic
acids ................................................................................................................................ 114
Table 5-2 Summary of metabolites detected from the degradation of CHCA by
Xanthobacter sp. and CHPA by Pseudomonas putida growing on these substrates as
their only carbon source. ................................................................................................ 117
Table 6-1 List of genes used for qPCR and their corresponding enzyme and metabolic
activity. ........................................................................................................................... 127
Table 6-2 Designed primer sequences to test for optional qPCR amplification of dsrB, sox,
and mcrA genes based on the pond 6 (2008/2010) metagenome. .................................. 129
Table 6-3 real time PCR program for each particular gene .................................................... 132
Table 6-4 Set of primers selected for functional gene study in tailings and their optimal
annealing temperature (Ta), amplicon size, and copy number obtained from each
reference organism. ........................................................................................................ 134
Table 6-5 Average percent of functional genes normalized to the total 16S rRNA genes.. ... 137
Table 7-1 Tailings enrichments amended with naphtha (0.5 vol %) or NAs (20 mg · L-1)
under methanogenic or sulfate-reducing conditions. ...................................................... 155
xii
Table 7-2 Tailings enrichment experiment using naphtha (0.5 %) as the carbon source with
nitrate and/or sulfate as the electron acceptors added at 5 or 10 mM. ........................... 157
Table 0-1 Microbial rank identified in pond 6 2008 .............................................................. 208
Table 0-2 Microbial rank identified in pond 6 2010 .............................................................. 209
Table 0-3 Microbial rank identified in pond 6 2011 .............................................................. 210
Table 0-4 Microbial rank identified in pond 5 2009 .............................................................. 211
Table 0-5 Microbial rank identified in pond 5 2010 .............................................................. 212
Table 0-6 Taxonomic classification and estimated richness for pond 6 samples using 95%
similarity values .............................................................................................................. 214
Table 0-7 Taxonomic classification and estimated richness for pond 5 samples using 95%
similarity values. ............................................................................................................. 216
Table 0-8 Taxonomic classification, observed and estimated richness for TPW samples
using 95% similarity values. ........................................................................................... 218
xiii
List of Figures and Illustrations
Figure 1-1 Map of Alberta showing the oil sands surface mineable area of 4, 800 km2 of
which 715 km2
of land has currently been disturbed 1. ....................................................... 2
Figure 1-2 Bitumen extraction scheme by surface mining technology. ..................................... 5
Figure 3-1 Schematic representation of the zinc acetate trap for SRR determination.. ........... 41
Figure 4-1 Aerial view of Suncor ponds 5 and 6. Image courtesy of Suncor Energy Inc. ....... 57
Figure 4-2 Flow diagram of Pond 6 management activities during the years 2008 to 2011.
Based on personal communication with Suncor Energy Inc. ........................................... 60
Figure 4-3 Most common microbial members found in Suncor pond 6 tailings at (A)
phylum level, (B) genus level, and (C) total average of most common genera in the
three years sampled. ......................................................................................................... 64
Figure 4-4 Depth dependent profile of most abundant percentage of pyrosequencing OTUs
in pond 6 at the genus level (A) in 2008, (B) in 2010, and (C) in 2011. .......................... 65
Figure 4-5 Distribution of selected microbial community composition at the genus level
(as % of pyrosequencing OTUs) found in Suncor pond 6 sampled in 2008, 2010, and
2011 as a function of depth. .............................................................................................. 66
Figure 4-6 Relational tree clustering for pond 6 samples (2008, 2010, 2011). Bray-Curtis
dissimilarity was used to calculate the distance. .............................................................. 68
Figure 4-7 NMDS diagram showing all oil sands tailings samples collected from pond 6 in
2008 (●), 2010 (♦), and 2011 (■). ..................................................................................... 69
Figure 4-8 Chemistry and microbial activity in pond 6 determined during the years 2008
(♦), 2010 (೦) and 2011 (∆). ............................................................................................... 72
Figure 4-9 Concept of Pond 5 reclamation strategy. (Courtesy of Suncor Energy Inc.). ........ 75
Figure 4-10 Views of pond 5 with geofabric and coke covering. (Image courtesy of Suncor
Energy Inc.) ...................................................................................................................... 76
Figure 4-11 Average of pyrosequencing OTUs in pond 5 in 2009 and 2010 . ........................ 78
Figure 4-12 Depth dependent profile of most abundant OTUs (> 3% of the total
community OTUs) in pond 5 at the genus level ............................................................... 80
Figure 4-13 Relational tree clustering for pond 5 samples (2009, 2010). Bray-Curtis
dissimilarity was used to calculate the distance. .............................................................. 82
xiv
Figure 4-14 NMDS plot of the two sampling times in pond 5 to illustrate their statistical
compositional difference. (●) pond 5 2009, (♦) pond 5 2010. .......................................... 83
Figure 4-15 Chemical characterization and microbial activity measurements of pond 5
before pond closure in 2009 (♦) and after pond closure in 2010 (೦). ............................... 86
Figure 4-16 A schematic of the dominant microbial processes found in Suncor’s oil sands
tailings pond 6 based on data obtained in this work. ........................................................ 89
Figure 4-17 NMDS of all tailings samples collected (pond 5 2009, 2010, and pond 6 2008,
2010, 2011) showing how samples collected in the same year cluster. ......................... 102
Figure 5-1 Sulfide loss over time in medium with 3 mM HS- and live or autoclaved
tailings. ........................................................................................................................... 109
Figure 5-2 Most abundant pyrosequencing OTUs in tailings surface water from pond 6
2008, pond 5 2009, and pond 6 2011. ............................................................................ 111
Figure 5-3 Relational tree for TPW samples (P62008, P52009, P62011). Bray-Curtis
dissimilarity was used to calculate the distance. ............................................................ 112
Figure 5-4 Time course biodegradation experiment............................................................... 115
Figure 5-5 Proposed biodegradation pathway of CHPA via -oxidation by P. putida strain
ER28.. ............................................................................................................................. 118
Figure 5-6 Mass spectra of metabolites detected (as silylated derivatives) after 3 d
incubation of Acidovorax sp. strain ER10 with CHAA .................................................. 119
Figure 5-7 Proposed biodegradation pathway of model NA cyclohexaneacetic acid by
Acidovorax sp. strain ER10.. .......................................................................................... 120
Figure 6-1 Gene copy number of specific genes (dsrB, mcrA, sox) per gram of tailings,
quantified in tailings samples from pond 6. ................................................................... 135
Figure 6-2 Correlation between qPCR of the functional genes (dsrB, mcrA, sox), in pond 6
2008. ............................................................................................................................... 139
Figure 6-3 Correlation between qPCR of the functional genes (dsrB, mcrA, sox), in pond 6
2010. ............................................................................................................................... 141
Figure 6-4 Correlation between qPCR results of the functional genes (dsrB, mcrA, sox), in
pond 6 2011. ................................................................................................................... 142
Figure 6-5 Proposed mechanism of microbial interaction between Desulfocapsa sp and
Thiobacillus sp. occuring in oil sands tailings ponds. .................................................... 148
Figure 7-1 Appearance of enrichments after each transfer (done ~ every 150 days). ............ 154
xv
Figure 7-2 Monitoring of methane production by enrichments amended with naphtha or
natural NAs to enrichments with tailings from 6 and 22 mbs from pond 6 2010. ......... 160
Figure 7-3 Methane production and sulfate depletion observed after the third transfer of
tailings enrichments with natural NA or naphtha as carbon sources using samples
collected from 6 and 22 mbs of Suncor Pond 5. ............................................................. 162
Figure 7-4 Microbial community analysis of tailings enrichments from pond 5 (2010)
samples identified at the genus level after the third tranfer of NA and naphtha-
amended enrichments. .................................................................................................... 165
Figure 7-5 Enrichments with naphtha as the electron donor and nitrate or sulfate as the
electron acceptor. Methane, sulfate, nitrate, and nitrite levels in enrichments
containing (A) 5 mM nitrate, or (B) 10 mM nitrate. ...................................................... 168
Figure 7-6 Enrichments with naphtha as the electron donor and nitrate and sulfate as the
electron acceptor. Methane, sulfate and nitrate measurements in incubations
containing (A) 5 mM nitrate, 5 mM sulfate, (B) 10 mM nitrate, 5 mM sulfate, (C) 5
mM nitrate, 10 mM sulfate. ............................................................................................ 169
Figure 7-7 Percentage of pyrosequencing OTUs present in tailings enrichments with no
added electron acceptor or with nitrate and/or sulfate added as electron acceptors. ...... 171
Figure 7-8 Microbial processess in Suncor oil sands tailings pond 6 2010. .......................... 178
Figure 7-9 Schematic representation of the displacement of SRB by hNRB when nitrate is
available in tailings ponds. ............................................................................................. 180
Figure 7-10 Proposed model of microbial community shifts when nitrate and/or sulfate is
added as alternate electron acceptors to tailings (pond 5 2010) amended with
naphtha. ........................................................................................................................... 184
Figure 0-1 Rarefaction curves for the microbial community of Suncor pond 6 in the years
(A) 2008, (B) 2010, and (C) 2011. ................................................................................. 215
Figure 0-2 Rarefaction curves for the microbial community of Suncor pond 5 in the years
(A) 2009, (B) 2010. ........................................................................................................ 217
Figure 0-3 Rarefaction curves for the microbial community in TPW. ................................... 219
Figure 0-4 Sulfur metabolism in tailings ponds obtained by metagenomics. ........................ 220
Figure 0-5 Iron concentration (Fe (II)) determined by the Ferrozine assay 213
in oil sands
tailings. (A) pond 6 sampled in 2011, and (B) pond 6 sampled in 2012. ....................... 221
sp.sp.sp.
xvi
List of Symbols, Abbreviations and Nomenclature
Symbol Definition
µCi 10-6
Ci, 1Ci= 3.7 × 1010
Bq
A absorbance
ANME anaerobic methanotrophs
AOM anaerobic oxidation of methane
BTEX benzene, toluene, ethylbenzene, and xylenes
CHAA cyclohexaneacetic acid
CHCA cyclohexanecarboxylic acid
CHPA cyclohexanepentanoic acid
cpm counts per minute
CT consolidated tailings or composite tailings
DCM dichloromethane
dsrB dissimilatory sulfite reductase gene
EPS extracellular polymeric substances
ERCB Energy Resources Conservation Board
HS-, H2S sulfide
Kan kanamycin
LB Lysogeny broth
MBH Modified Bushnell - Haas salt solution
mbs meters below surface
mcrA subunit of methyl coenzyme-M reductase
MFT mature fine tailings
MLSB Mildred Lake Settling Basin
mM millimolar
MPN most probable number
NA(s) naphthenic acid(s)
NMDS nonmetric muldimensional scaling
xvii
NTC no template control
OD optical density
OTU operational taxonomic unit
PAH(s) polycyclic aromatic hydrocarbons
PCR polymerase chain reaction
qPCR quantitative PCR
rRNA ribosomal RNA
SEM scanning electron microscopy
SOB Sulfide-oxidizing bacteria
sox sulfite oxidase genes
SRB Sulfate-reducing bacteria
SRR sulfate reduction rate
Ta annealing temperature
TPW tailings process water
TRO tailings reduction operations
1
Chapter One: Literature Review
1.1 Oil sands tailings pond formation
1.1.1 Surface mining for bitumen extraction
Canada is home to the world’s third largest oil reserve after Saudi Arabia and
Venezuela 1. This reserve is found mainly in north-eastern Alberta covering an area of
approximately 142, 200 km2 divided in 3 regions: Athabasca, Cold Lake, and Peace
River 1. With 170 billion barrels of proven bitumen reserve (proven reserve refers to a
known mineral resource that can be recovered economically using existing technologies),
only 3% of the total reserve (4, 800 km2) can be surface mined because the bitumen is
found very close to the surface, between 60 to 80 meters 2. To date, approximately 715
km2 of land has been disturbed for mining activity
1,3 [Figure 1-1].
Alberta’s oil sands industry began commercial operations in 1967 pioneered by the
Great Canadian Oil Sands, today known as Suncor Energy Inc., and later followed by
Syncrude in 1978. Currently, more than 40 companies operate in the oil sands 4. In 2010,
Alberta produced 1.6 million barrels of bitumen per day mainly by in situ technology
(SAGD: steam-assisted gravity drainage) and production is expected to increase to 3.5
million barrels per day by 2020 1.
2
Figure 1-1 Map of Alberta showing the oil sands surface mineable area of 4, 800
km2 of which 715 km
2 of land has currently been disturbed
1.
3
The oil sands are a mixture of solids, bitumen and water. The solids, or mineral
content, which is the major component in the oil sands (85 wt %), varies in its
composition but it is mainly composed of quarts, silts, and clays. The clay content is
predominantely kaolinite, illite, illite-smectite, kaolinite-smectite, montmorillonite, and
chlorite, with the first two being the most abundant in the Athabasca region 3,5,6
. An
average of 12 wt % of bitumen can be found attached to these minerals together with
water. The latter accounts for 3 – 6 wt % 3,7
.
The open pit mining extraction method can recover approximately 88 to 95 % of
the mineral-trapped bitumen 8. The process involves using water, mechanical energy and
chemicals such as sodium hydroxide 2,3
. The bitumen is separated from the sand, clays
and other impurities by the Clark extraction method which uses hot water (79–93C) and
caustic soda 9,10
. This extraction procedure is possible due to the hydrophilic
characteristic of the oil sands 3. They consist of water-wet sand particles where the oil is
found in the void spaces and not in direct contact with the mineral grain because it is
surrounded by a thin layer of water 3,11
. For an average sand grain of 100 µm of diameter,
a water film of 2.0 µm can be found 3,11
.
The hot water treatment reduces the viscosity or thickness of the bitumen and the
caustic soda helps the detachment of bitumen from the sand particles. Naphthenic acids
(NA), naturally present in oils, including oil sands, act as surfactants and help separate
the bitumen from the sand 3. The mixing of oil sands and caustic hot water takes place in
big drums and the slurry formed passes through a series of vibrating screens until the
slurry is finally pumped into separation tanks. The primary separation vessel allows the
4
oil sand slurry to settle out into various layers with bitumen-containing layer situated at
the top of the tank. The sand sinks to the bottom and together with excess water is
pumped into a pipe which carries it to the tailings ponds. The described procedure is
repeated with the middle layer from which another 2 to 4 % of bitumen can be extracted.
In the final steps, diluents (e.g. naphtha) are added as a diluent to decrease viscosity and
to help in the separation of the remaining bitumen from the sand. Once again, the slurry
of water, sand and clay is carried through pipelines into the tailings ponds. This time,
some of the naphtha is present in the slurry composition 3,11
. Figure 1-2 summarizes the
whole process described above. Some operators (e.g., Shell Albian Sands) use aliphatic
C5 – C6 as a diluent to help detach the bitumen from the sand in the extraction process 12
.
This slurry is the so-called tailings: a mixture of water, clay, sand, and residual
bitumen and hydrocarbon diluents. There are three main sources of tailings derived from
the extraction process: (1) coarse tailings, (2) fluid fine tailings, and (3) froth treatment
tailings 2. The coarse tailings are mainly sand. Fine tailings are mineral particles less than
44 µm and froth accounts for only a small stream mainly composed of water, sand, fines,
residual bitumen and solvents 2.
Due to the zero discharge policy, tailings are stored in settling ponds where the
recycling of the water into the extraction process, and ultimately the restoration of the
site, are the main goals 13,14
. Today, up to 90 % of the water is recycled, thus significant
reduction of fresh water consumption for bitumen surface mining has been accomplished
4. Typical ponds can comprise areas ranging from 2.5 to 25 km
2 and have an average
depth of 50 meters below surface (mbs) 15,16
.
5
Figure 1-2 Bitumen extraction scheme by surface mining technology. The mined oil
sands are transported to the extraction plant where bitumen is separated from the
sand by the Clark alkaline hot water method. The tailings produced are transported
through pipelines to the settling ponds where solids are allowed to settle so that the
water can be recycled back into the extraction process.
MFT
WATER
Sanddyke
Beach sand
Sanddyke
Open pit mine
Extraction plant
Froth treatment
bitumen froth
Recy
cled
wat
er
• Chemicals• Hot water (raw water)• Steam• air
oil sands
Make up solvent (naphtha)
(bitumen, solids, water)
bitumenRefinery
Tailings• Water• Solids• Unrecovered solvent• Unrecovered bitumen
Tailings• Water• Solids• Unrecovered bitumen
6
1.1.2 Tailings pond composition
Tailings composition varies depending on the depth and age of the pond, on the
source of the ore from which bitumen was extracted, as well as on the extraction process
used 17,18
. In general, tailings have varying proportions of minerals, water, dissolved
organic and inorganic salts, and residual organics including bitumen and hydrocarbon
diluents. About 55 wt % solids are found in a typical tailings pond, of which 82 wt % are
sand particles larger than 45 µm, 17 wt % are fines (< 44 µm or smaller), and 1 wt % is
residual bitumen 3.
In the process of sedimentation, tailings ponds become stratified into 3 main layers:
the rapidly setting sand particles that form a beach, an aqueous suspension of fine
particles, composed mainly of silt and clay, and a clarified surface water layer also
known as TPW (tailings processed water) or process-affected water (PAW) that contains
total suspended solids, residual diluents, and bitumen 19
. The immediate contact of the
fine particles in suspension to the TPW is known as the mud line. This line divides the
pond into the surface, mostly aerobic (TPW) and the anaerobic zone (tailings).
The fines in the aqueous suspension are derived from the clay present in oil sands,
thus their mineralogy is very similar: kaolinite (22 -76%), illite (7 – 10 %) and
montmorillonite (1-8 %) 18
. Trace amounts of chlorite, quartz, iron oxides, and varying
amounts of amorphous material can also be found 17,18
. This clay mixture forms a stable
suspension that, after 2 to 3 years, settles into a fluid-like deposit called Mature Fine
Tailings (MFT), made of about 30% solids and 65% water, and 5% bitumen. Under
7
current technology, the production of 1 m3 of synthetic crude generates 6 m
3 of sand and
1.5 m3 of MFT
14,20.
Approximately 12 barrels of water (1428 L) are needed to extract 1 barrel of
bitumen from the oil sands but because much of the water is recycled, only 3 – 5 barrels
need to be replaced by fresh water input 2. In total, the tailings generated represent about
1.4 times the original volume of the oil sands 2. In fact, current estimates of the total
MFT inventory lies between 270 and 1000 million m3, occupying an area of more than
170 km2 in tailings ponds
2,4.
The MFT contains a substantial content of organic matter derived primarily from
unrecovered bitumen. The bitumen content varies from one pond to the other. For
instance, Syncrude’s Mildred Lake Settling Basin (MLSB) may contain between 0.7 and
2.0 % of total mass whereas Suncor ponds could have between 0.3 and 5.0 % 17
. This
organic matter was classified by Kasperski (1992) 18
into three categories: (1) residual
bitumen, (2) soluble compounds, and (3) mineral-associated compounds. The residual
bitumen (1) refers to the unrecovered bitumen from the Clark extraction process. About
10 to 15 % of the bitumen is trapped in the tailings sand and approximately 25 to 30 % is
dispersed in the tailings 18
. The bitumen content in the tailings can range from 1 to 5 wt
% depending on the depth where higher content will be found at deeper layers 18
. Soluble
compounds (2) comprise those compounds that are dissolved in the water during the
extraction process. In the water phase, these organic compounds can range between 100
and 120 mg · L-1 of which around 55 % are organic acids
18. In the tailings fraction, these
compounds are mainly polar, humic/fulvic acid-type compounds. Others like alkyl
8
phenols, polyphenolic aromatics, and polycyclic aromatic hydrocarbons (PAHs) are also
found 18
. Finally, the mineral associated-compounds (3) include a variety of compounds
composed of a mixture of fulvic and asphaltic acids probably fixed to clay particles
through iron III linkage (Fe3+
) 18
.
It is believed that the rate at which MFT naturally consolidate could take about 125
to 150 years to be completed 16
. One of the main reasons is due to the presence of
approximately 3 % of ultrafines (colloidal phyllosilicate clays with dimensions < 0.3 µm)
and the type of clay and its swelling capacity. The ultrafines form a gel-type structure
with adequate internal volume capable of accomodating all of the water from the mature
tailings 21,22
. Consequently, the continuous coarse solids that are carried into the pond
become captured within this gel to finally produce the 30 wt % solids that are observed in
this layer 21
. This structure is also closely dependent on the amounts of electrolytes and
the types of anions present in the water 22
. In addition, the kaolinite and/or iron oxides
present in the bitumen-clay interactions, together with the humic/fulvic acid compounds
tightly bound to fines, in the presence of caustic soda, possess an enhanced negative
surface charge which promotes dispersion of the particles, inhibiting their sedimentation
and consolidation 3,6,23,24
.
To overcome the slow consolidation rates, some oil sands operators (e.g., Suncor
and Syncrude) have been using the non-segregating tailings technology by adding
densification reagents such as calcium sulfate (gypsum) to the MFT and mixing it with
sand, at a sand-to-fines ratio of approximately 4:1 25
. Other operators, such as Shell
Albian Sands, use other coagulants such as polyacrylamide 12
. The process is also known
9
as Consolidated Tailings (CT) or Composite Tailings 14
. The addition of Ca2+
as a
flocculating agent markedly improves the settling characteristics 26
. The Ca2+
allows for
the aggregation of fines due to an increase in the adhesion force between the fine
particles 27
. About 1 kg of CaSO4 · m-3
tailings are added to produce CT 3,28
. However,
concerns with CT technology using gypsum are: (1) accumulation of Ca2+
in the
recovered processed water can lower bitumen recovery efficiency 3, and (2) that sulfate
(SO42-
) ions in the TPW can accumulate and under anaerobic conditions be biologically
reduced to sulfide leading to the production of hazardous H2S gas. Other coagulants can
also be used but gypsum is more readily available as it is a byproduct of the oil industry
3.
Apart from diluents (e.g. naphtha) and bitumen, NAs can also be found in tailings
ponds. These compounds, naturally present in the oil sands, are classically defined to be
water soluble complex mixtures of alkyl-substituted acyclic and cyclic aliphatic
carboxylic acids with the general formula of CnH2n+Z O2 , where n indicates the carbon
number and z indicates the hydrogen deficiency due to ring formation. The z value
divided by 2 gives the number of rings present in the compound 29,30
. However, high
resolution analysis of NAs obtained from petroleum have shown the presence of pyrroles,
thiophenes, and phenols. Some do not even have the carboxylic acid functional group but
instead they contain heteroatoms such as sulfur and nitrogen 29
. These chemicals are
solubilized during the bitumen extraction process 31
and as mentioned earlier, act as
surfactants under alkaline conditions to help separate the bitumen from the sand 3. NA
can reach concentrations as high as 100 mg · L-1
in TPW 32-34
. They are known to be
10
toxic to a variety of aquatic organisms, algae, invertebrates, mammals and some
microorganisms, thus representing a great environmental concern 35,36
.
Finally, another important component in tailings ponds is microorganisms. Tailings
are known to harbour an active microbial community 15,37-40
. These are presumably
supported by the presence of the previously mentioned organic compounds and others
such as asphaltenes, benzene, phenols, toluene, creosols, humic and fulvic acids, and
PAHs. The ponds also contain calcium, sodium, chloride, sulfate, bicarbonate, and
ammonia 19
. All these chemicals support the presence of syntrophs, fermentative bacteria,
sulfate-reducing bacteria (SRB) and methanogens, which are abundant microbes in the
anoxic layers. These groups of microorganisms are responsible for the methane and
sulfide gas emissions that have been reported to evolve from tailings ponds 16,41,42
.
Nevertheless, the surface water also sustains the growth of aerobic bacteria and algae that
are dynamically related to the shallower anoxic layers of the pond. In general, despite the
toxicity, tailings ponds contain a vast and interesting microscopic world that can be
revealed using modern molecular biology tools. More details regarding microbes in
tailings ponds will be discussed in section 1.2.1.
1.1.3 Tailings pond management and environmental concerns
Despite attempts to reduce the negative effects of the mining operations by
improving tailings management and by finding new cleaner technologies, tailings ponds
continue being the focus of attention by both the media and the Canadian government.
On average, 375,000 m3
of MFT per day are discharged into the settling ponds,
considering that every cubic meter of synthetic crude generates 1.5 m3
of MFT per day.
11
As these waste streams flow into the pond, the available oxygen is readily consumed by
the existing microbiota. Subsequently, as layers of tailings are deposited, less oxygen is
available due to the low permeability of the sedimented layers, thus resulting in mainly
anoxic ponds 43
. Consequently, anaerobic Bacteria and Archaea tend to dominate these
ecosystems from 1 to 60 mbs 37,41,44-47
.
One of the main anaerobic bacterial groups in tailings ponds whose activity can
lead to gas emissions is the sulfate-reducing bacteria (SRB). Due to the addition of
gypsum, SRB become enhanced and favoured thus increasing the risk of hydrogen
sulfide (H2S) release into the atmosphere. However, given the slight alkaline pH of the
tailings, most sulfide is present as HS- which most likely precipitates as iron and other
metal sulfides or pyrite (FeS2) 16
. Moreover, the fraction of sulfide that is not precipitated
could be potentially oxidized to sulfur and sulfate. Therefore, only a small fraction of
H2S emissions from CT deposits could be expected 44
. In anaerobic experiments with
tailings, only 3% of the total amount of SO42-
reduced was detected as free sulfide 16
. If
the pH in the pond becomes acidic, the metal sulfides would dissolve resulting in the
generation of H2S gas 16
.
Another important group of microorganisms in tailings ponds are the methanogens.
When sulfate drops to below 20 mg · L-1, methanogens prosper, which can lead to the
release of significant amounts of methane to the atmosphere 31,44
. Previous studies have
shown that a typical pond can release a daily flux of 12 g of CH4 per m2 46
. Since
methane is a greenhouse gas and emissions can enhance the volatilization of lower
molecular weight hydrocarbons, this represents a serious environmental concern 16
.
12
Water management in tailings ponds may be an issue. The continual recycling of
the water to the extraction plant can lead to an increase of dissolved ions that cause
various operational problems, including poor extraction recovery together with
scaling/fouling of piping and equipment 25
. On the other hand, as NAs become
solubilized and concentrated in the TPW their persistence in the ponds becomes an
environmental threat due to acute and chronic toxicity to various organisms 36,48
.
Oil sands tailings ponds operators are enforced to comply with certain
environmental rules and directives in order to lower the environmental impact produced
by their operations. These sites are being continuously monitored for air and groundwater
quality, as well as control of the volumes of tailings produced 4,49
. In February 2009, the
Energy Resources Conservation Board (ERCB) developed the tailings management
regulations Directive 074 50
. This directive states that companies are required to reduce
tailings and provide target dates for closure and reclamation of ponds. It also sets out
timelines for operators to process fluid tailings at the same rate they produce them, in
order to prevent the volumetric growth of the ponds 50
.
Other operators search for cleaner technologies in order to comply with the
established environmental targets. Such is the case of Suncor Energy Inc. which has
recently started to implement a new technology for tailings management. The approach
called the TRO (Tailings Reduction Operations) significantly improves the speed of
tailings reclamation by converting fluid fine tailings more rapidly into a solid landscape.
In this process, MFT is mixed with a polymer flocculant, and then deposited in thin
layers over sand beaches with shallow slopes where it is allowed to dry in a matter of
13
weeks. The resulting product is a dry material that is capable of being reclaimed in place
or moved to another location for final reclamation 51
. The closure of ponds with several
layers of coke when they become full to capacity is another strategy followed by Suncor
Energy Inc. 52
.
Managing oil sands tailings is of great concern to Canada and has led to the
development of the Oil Sands Tailings Research Facility (OSTRF), which is dedicated to
collaborative and multi-disciplinary tailings research 25
. Others like the Oil Sand Tailings
Consortium (OSTC) founded in 2010, collaborates on research and development related
to tailings by reflecting the companies’ commitment to socially and environmentally
responsible operations. More recently, at the beginning of 2012, Canada's oil sands
producers formed a new alliance, Canada's Oil Sands Innovation Alliance (COSIA),
focused on accelerating the pace of improving environmental performance in Canada's
oil sands.
In general, the Alberta government together with the industry and academic
institutions continues to provide financial and other resources to improve the tailings
management with the final aim of reducing the oil sands operational footprint.
1.2 Microbiology of tailings ponds
1.2.1 Tailings ponds: a niche for microbial activity
Despite the toxicity of oil sands tailings, the ponds harbor a varied community of
microorganisms 37,45,46
. These were initially believed to come from the Athabasca river
(source of fresh water for the bitumen extraction process by the Clark method) as
14
bacterial activity was found in the extraction streams discarded to the ponds, even those
at high temperature 18
. However, a recent 16S rRNA gene-based study of the microbial
population present in the Athabasca river and its sediment revealed that the microbial
communities in fine tailings were distinct from those in the river and its tributary
sediments 53
. These results may imply that tailings ponds harbor a unique microbial
community that could have initially originated from the river, the pipelines, and the oil
sands themselves; but once they reach to the pond, and as the pond ages, these organisms
start interacting with each other (e.g. gene transfer), and start expressing metabolic genes
depending on the substrate availability. Thus those microbes possessing better
adaptability to tailings conditions will prevail.
It is thought that tailings microorganims may be predominantly found in the pond
adhered to the clay or sand particles promoting tailings aggregation, thus contributing to
densification 15
. In fact, species like Pseudomonas, Thauera, Hydrogenophaga,
Rhodoferax, and Acidovorax, detected in the pond have the ability to grow in a biofilm
structure, presumably attached to the mineral matter 38
. This arrangement allows
microbes to survive the tailings toxicity and improves the absorption of the nutrients
available.
The bulk of a tailings pond is mostly anaerobic. Hence, the majority of microbial
activity is carried out by anaerobic Bacteria and Archaea. In the absence of oxygen,
certain compounds like nitrate (NO3-), ferric iron (Fe
3+), SO4
2- and CO2 can be used as
terminal electron acceptors 54
. These can be reduced by many organisms in a
dissimilatory way to provide energy for their metabolism. Microorganisms are classified
15
based on the type of electron acceptors they use; hence, nitrate reducers use NO3-, iron
reducers use Fe3+
, sulfate reducers use SO42-
and methanogens can use CO2 54
. The
energy released from the oxidation of an electron donor using these compounds as
electron acceptors varies. Each electron acceptor has different reduction potentials that
make them more or less energy efficient based on their electronegativity. Therefore,
nitrate reduction is the most energy-yielding followed by iron, then sulfate, then
methanogenesis 54
.
1.2.1.1 Sulfate-reducing bacteria (SRB) and methanogens
In some tailings ponds, SO42-
is readily available in fresh tailings due to the
gypsum addition used to enhance tailings densification. The sulfate concentrations in
tailings ponds typically decrease with depth 46
, with the highest sulfate concentration
found at the surface waters between 150 to 170 mg · L-1 , or as high as 576 mg · L-1
55
.
The use of SO42-
as an electron acceptor by SRB results in the production of HS- at
slightly alkaline pH values 54
. This sulfide release becomes a problem when its
production exceeds the amount of metals available for the formation of metal sulfides or
if the pH drops markedly in the pond . In addition, the amount of sulfate reduced depends
on the bioavailability of the electron donors. SRB can be found in tailings at an average
MPN (most probable number) of 109 · g of MFT for Suncor and Syncrude tailings
16,44.
As a pond ages, the sulfate levels in the anaerobic layers decrease and the pond
becomes methanogenic 44
. A clear example of this is reflected by studies carried out in
MLSB, the primary tailings pond managed by Syncrude Canada Ltd., where methane
16
was not detected in the first 15 years of operation. For these initial years the SO42-
concentrations were between 35 – 75 mg · L-1 for the deep layers and between 60 – 120
mg · L-1 at shallower depths
44. However, by the mid-1990s, methane bubbles were
visible on the surface of the MLSB and this corresponded with a drop in sulfate
concentrations to values as low as 5 mg · L-1 in the year 1997
16,44. In 2000, Holowenko et
al.46
detected 105 – 10
6 methanogens and 10
4 – 10
5 SRB · g-1
of MLSB tailings. Because
both types of organisms can compete for the same electron donors, with SRB catalyzed
reactions being more energetically favorable, the presence of SO42-
can inhibit or delay
the production of methane 46
[Reactions 1, 2, 3, 4]. This is true as long as electron donors
are not abundant, in which case methanogens manage to sequester a portion of the
electron flow even when SO42-
is present to support SRB 44
.
Reactions catalyzed by SRB and methanogens
Competition for H2 is a very common feature in anaerobic environments. Hydrogen
is usually readily produced and consumed, so its level remains relatively low in the
natural environment. SRB consume H2 more efficiently than methanogens thus
maintaining concentrations too low for methanogens [Reactions 1, 3]. The same pattern
4H2 + SO42- + H+ HS- + 4H2O ∆G = - 152 kJ · reaction-1 [1]
CH3COO- + SO42- HS- + 2HCO3
- ∆G = - 47 kJ · reaction-1 [2]
4H2 + HCO3- + H+ CH4 + 3H2O ∆G = - 135 kJ · reaction-1 [3]
CH3COO- + H2O CH4 + HCO3- ∆G = - 31 kJ · reaction-1 [4]
17
is observed when Fe3+
is available. Iron reducers can use H2 thus decreasing its
concentration to levels below the threshold for either SRB or methanogens 54
.
Methanogens are strict anaerobes that produce methane when growing on H2/CO2,
formate and other substrates like acetate, methanol, ethanol, isopropanol, methylated
amines, and methylated sulfur compounds 56
. Some methanogens such as
Methanobrevibacter sp. can only use H2/CO2, others like Methanosaeta sp. can only
grow on acetate. Others are somewhat more flexible and can grow on H2/CO2 and
formate like Methanospirillum sp. and Methanobacterium sp. or like Methanosarcina sp.
that can grow on H2/CO2, acetate, methanol and a few other carbon compounds 56
.
Methanogens rely on other bacteria, such as syntrophs or acetogenic bacteria, to
degrade complex hydrocarbons to their simple substrates. SRB can also collaborate with
the syntrophs to degrade hydrocarbons 57
. Overall, competition for substrates in the pond
can lead to the inhibition of some groups of microorganisms like methanogens in the
presence of sulfate [Figure 1-3]. However, because tailings can supply other electron
donors for syntrophs, methanogenesis can still be active and methane can eventually
evolve from the deep anaerobic zones towards the surface layers 44
.
1.2.1.2 Iron reducing bacteria (IRB)
In tailings ponds iron comprises around 3% of the solids 44
. Iron can fluctuate between
ferrous (Fe2+
) and ferric (Fe3+
) forms and their concentrations have been determined to be
relatively low ( 0.8 mg · L-1 in Syncrude tailings)
16. The predominance of one form of
iron over the other depends greatly on environmental physicochemical parameters such
18
as pH, oxygen concentration and redox potential 58
. Due to the slight alkalinity of tailings
(pH 7 - 8) and to the abundance of sulfate, one would expect to find iron as FeS or as
FeS2 16
. The total number of iron reducers in Syncrude tailings were found in the range of
101
- 10 5 cells · g-1
of MFT as determined by MPN 44
, lower than the numbers of SRB,
NRB, and methanogens found in the same pond 16
. Different groups of bacteria have
been studied for their ability to either reduce or oxidize iron compounds. Such is the case
of Thiobacillus denitrificans, a strict autotroph that has been known for its ability to
oxidize pyrite in the presence of nitrate in anoxic sediments 59
or Acidovorax sp. that can
oxidize ferrous iron in the presence of organic acids such as acetate 58
.
19
Figure 1-3 Schematic representation of the degradation of hydrocarbon compounds
under anaerobic conditions. Oil hydrocarbons are attacked by (1) acetogenic
bacteria to produce acetate or by (2) syntrophs to produce H2, CO2, and/or acetate.
In the absence of electron acceptors acetoclastic methanogens are favored (3) but
when sulfate is available SRB (5) compete with methanogens for acetate. Similarly
SRB can compete for H2 (6), but when no sulfate is available, hydrogenotrophic
methanogens (4) utilize H2 with the concomitant production of methane. SRB can
also directly oxidize selected oil components with sulfate (7).
CH4 CO2
Acetogenicbacteria
Syntrophicbacteria
Acetate H2 + CO2
Acetoclasticmethanogens
Hydrogenotrophicmethanogens
Sulfate reducing bacteria (SRB)
SO42-
H2 S
CO2 H2O
CH4
SO42-H2 S
CO2
SRB
Hydrocarbon compounds
(1) (2)
(7)
(3)
(5) (6)
(4)
20
1.2.1.3 Nitrate reducing bacteria (NRB)
Other groups of microbes also detected in tailings ponds are the nitrate-reducing
bacteria (NRB) . Nitrate has been found in Syncrude tailings concentrations of 16 mg ·
L-1
. In a laboratory experiment, the NO3- disappeared after 36 days of incubation
suggesting that it was converted to either N2 or N2O by denitrifying bacteria which were
initially present in the tailings samples at a concentration of 108 cells · g-1
of MFT 16
, or
converted into biomass.
A positive outcome of the presence of NRB in the pond is their ability to form
biofilm and/or aggregates of clay particles that contribute to tailings densification 15,38
.
Simultaneously, if nitrate were to be present in adequate proportions in the pond, this
could help in controlling H2S emissions, if any, in the same way that nitrate is used to
control souring in oil fields 57
.
1.2.1.4 Aerobic microorganisms in tailings ponds
Tailings ponds also support a group of aerobic and facultatively anaerobic bacteria
that grow at the surface of the pond, where oxygen and other nutrients are available.
However in earlier studies by Foght et al. 37
, the microbiology of a Syncrude pond
revealed that bacteria with known aerobic and facultatively anaerobic respiration were
distributed from 0.5 to 12 mbs. Cell concentrations of 1.2 to 1.6 x 106 cells · mL
-1 were
detected with Alcaligenes and Acinetobacter being the most common genera found 37
.
21
These bacteria may be growing at the expense of solubilized organic matter or may
be playing important roles in utilizing the final products of the anaerobic microbes found
at the anaerobic/aerobic interface. Such is the case of methanotrophs. This group of
aerobic bacteria is capable of metabolizing methane as a source of carbon and energy 54
.
It has been observed that the methane produced by methanogens travels to the surface of
the pond as a bubble 45
. During its ascent, the bubble partitions other materials, carrying
them to the surface. For instance, oxygen can be incorporated into the bubble enhancing
the anaerobic nature of the deep layers of the pond 60
. Other gases, particles, oils,
bacteria, volatile hydrocarbons, and surfactants can also be partitioned into the bubble,
thus providing an important vertical transport mechanism 60
. Once the bubble reaches the
oxic layers, it can burst and microbes inhabiting this area benefit from the nutrients
released. For example, methanotrophs found in TPW potentially can use methane and
convert it to CO2, while sulfide-oxidizing bacteria (SOB) can use H2S and convert it to
sulfate. This interdependence may be beneficial as less methane and H2S can escape to
the atmosphere.
The oxidation of sulfur compounds by microorganisms is one of the oldest
metabolic mechanisms known and it is a process that is found tightly related to other
biogechemical cycles like carbon, oxygen and nitrogen in marine sediments 61
. SOB or
SOP (Sulfur Oxidizing Prokaryotes), are mainly composed of aerobic lithotrophs or
anaerobic phototrophs 62
. Apart from H2S, these organisms can oxidize sulfur, sulfite,
thiosulfate and various polythionates under alkaline, neutral, or acidic conditions with
sulfate as their final oxidation product 62
. Aerobic bacteria with this activity include
22
Acidaunus, Acidithiobacillus, Aquaspirillum, Aquifex, Bacillus, Beggiatoa,
Methylobacterium, Paracoccus, Pseudomonas, Starkeya, Sulfolobus, Thermithiobacillus,
Thiobacillus, and Xanthobacter 62
. Anaerobic phototrophs include Allochromatium,
Chlorobium, Rhodobacter, Rhodopseudomonas, Rhodovulum and Thiocapsa as the major
genera described to date 62
. Members of the order Sulfolobales (Archaea), are also known
to oxidize reduced sulfur compounds 63
. Two major biochemical pathways have been
proposed to oxidize the sulfur compounds: (1) the sulfur oxidation pathways, and (2) the
sulfite intermediate pathway 61
. The sulfur oxidation pathway (1), also called the Sox
system, oxidizes sulfur compounds directly to sulfate without the formation of sulfite
54,61. The sulfite intermediate pathway (2) can be observed in two different ways. The
most common pathway is that employing the enzyme sulfite oxidase 54
. The other is via a
reversal of the activity of adenosine phosphosulfate (APS) reductase, an enzyme present
in the metabolism of sulfate by SRB 54
.
As mentioned earlier, some aerobic bacteria may be metabolizing organic
compounds dissolved in the TPW such as NAs. Several studies have revealed the NA
degradation potential for indigenous tailings organisms 32,64-66
. For example, a mixed
culture of species enriched from tailings such as Pseudomonas putida and P. fluorescens
64 and P. stutzeri and Alcaligenes denitrificans
67 has been found to degrade NAs. More
details regarding NA biodegradation will be mentioned in section 1.2.2.
Independent of the metabolic processes ongoing at the surface of the pond, the
presence of these aerobic microorganisms may fluctuate depending on the months of the
year. Thus, during the wintertime, where a layer of ice tends to cover the ponds, these
23
populations may undergo a dormant state that can eventually be restored during the
summer time.
1.2.2 Sources of carbon for organisms living in tailings ponds
As previously summarized, tailings are a mixture of water, mineral and organic
matter that can support the metabolism of several living organisms. From eukaryotic
microbes to Bacteria and Archaea, they all find a place in which to survive and/or co-
exist. The specificity of electron donors used by microorganisms in tailings ponds is still
somewhat unknown. However, based on the chemical composition of tailings, some
assumptions can be made 44
.
For instance, a small fraction of naphtha (less than 1%) is lost to tailings and
incorporated into MFT, so this solvent could serve as a good source of electron donors.
In fact, the biodegradation of various n-alkane hydrocarbons under methanogenic
conditions has been previously demonstrated at the laboratory scale 41,47,68,69
. Some of the
microbial communities present in the MFT are capable of utilizing C6-C10 n-alkanes
under methanogenic conditions, which supports the hypothesis that components from
naphtha in oil sands tailings can sustain methanogenesis 41
. Experiments using BTEX
(benzene, toluene, ethylbenzene, and xylenes) amendments at 0.05% have also shown
that these compounds can be biodegraded under methanogenic conditions by tailings
microbes 47
. SRB have also been shown to metabolize toluene, xylenes, ethylbenzene and
naphthalene in other hydrocarbon-associated environments 70
.
24
Other studies regarding the use of long chain alkanes by anaerobic organisms have
also been carried out. Bacteria such as Syntrophus (a syntrophic bacterium), and
Desulfovibrio (a H2-utilizing SRB) have been found to be a part of alkane-degrading
consortia and methanogenic Archaea like Methanosaeta (acetoclastic methanogens),
Methanospirillum and Methanoculleus (methanogens utilizing H2 and CO2) have also
been detected in alkane-degrading cultures, and are presumably involved in converting
long chain alkanes to methane and CO2 by a process called microbial alkane cracking 71
.
More recently, the characterization of the microbial communities from tailings
enrichments involved in methanogenic biodegradation of naphtha and its short-chain n-
alkane (C6–C10) and BTEX components, revealed a syntrophic oxidation of hydrocarbons
in oil sands tailings 69
. The presence of bacterial genera such as Desulfotomaculum and
Syntrophus/Smithella together with the archaeal groups associated with Methanosaeta (in
n-alkane and naphtha enrichments) and Methanomicrobiales (in BTEX and naphtha),
suggests these organisms are involved as syntrophic partners in the degradation of these
organic compounds 69
.
Residual bitumen present in tailings should not be ruled out as a possible source of
carbon in tailings. Studies by Wyndham and Costerton 72
showed that saturates and
aromatic fractions from an Athabasca bitumen supported growth of some bacterial
isolates. They revealed, by the use of microscopy, that bacteria adhere to the hydrocarbon
surface making a bitumen-bacteria association with or without the formation of a
glycocalyx. When no polysaccharide is needed, the bacteria can be found within a few
micrometers of the bitumen surface or in channels penetrating the substrate 72
.
25
Last, but not least, NAs are other carbon sources present in tailings that can support
the growth of microorganisms. These natural compounds are extracted from the bitumen
during the Clark extraction process. They are commonly found at the aqueous/non-
aqueous interface of oil sands but because of the alkaline pH of tailings they are mainly
present as water-dissolved naphthenate salts that end up in the tailings ponds 31
. As
mentioned earlier, they are known for their acute or chronic toxicity to living organisms
36 and the degree of their toxicity has mainly been associated with their molecular weight
and surfactant characteristics. The higher molecular weight compounds with increased
carboxylic acid content will decrease hydrophobicity, thus becoming more bioavailable
and accumulating in the cells 32,36
. Their surfactant properties are thought to disrupt the
cell wall or membrane of the cells 73
.
Despite the toxic nature of NAs, experimental evidence to date indicates that NA
biodegradation is predominantly an aerobic process. Species like Arthrobacter,
Pseudomonas, Acinetobacter and Alcaligenes have been previously reported for their
ability to degrade NAs 74-78
. However, the persistence of NAs in tailings ponds is
believed to be high. The ongoing recycling of the water back into the bitumen extraction
plant tends to increase their concentration in the water, thus maintaining a steady
concentration in tailings 31,79
. On the other hand, it has also been suggested that NAs
could be derived from the action of microorganisms on the residual bitumen present in
tailings ponds, thus contributing to the total NA content 80
.
The mechanism under which biodegradation of NAs occurs is not well understood
but in general their susceptibility seems to be related to their molecular weight and the
26
degree of the branched alkyl chains 81
. Low molecular weight NAs are more
biodegradable than highly branched, high molecular weight compounds 32,82,83
.
Several pathways have been proposed for the degradation of aliphatic and alicyclic
carboxylic acids such as -oxidation, combined - and - oxidation, and aromatization
81,82. The -oxidation pathway seems to be the preferred route by which several bacteria
degrade these compounds 82
. For instance, the degradation of cyclohexanecarboxylic acid
by species including Acinetobacter anitratum, Alcaligenes faecalis and Pseudomonas
putida via -oxidation has been observed 75,77
.
In the anaerobic layers, the relatively high adsorption capacity of NAs to oil sands
solids allows them to sink to the bottom of the pond where little biodegradation can be
carried out. Even bitumen can act as trap for NAs, which would also contribute to their
retention throughout the vertical tailings column 79
. Higher molecular weight compounds
will be more strongly adsorbed to tailings particles than low molecular weight ones, and
this can decrease the bioavailability of these compounds to the microorganisms 31
. It is
not well known if NA can support growth in anaerobic environments. Previous studies
under methanogenic conditions with commercially available, natural NAs (extracted
from TPW), and surrogate NAs showed that methanogenic consortia present in a
Syncrude tailings ponds did not utilize NAs as their main source of carbon 84
.
Due to the complexity of the mixture of compounds in tailings, it is hard to
determine which substrates are preferred as electron donors for the pond microorganisms.
Also, the lack of available sources of nitrogen and phosphorus is thought to influence the
rate at which degradation of these complex compounds occurs 37,66
. As in any given
27
ecosystem, the species that most successfully inhabit it, are those best adapted to grow on
the nutrients and conditions available and tailings ponds are no exception 54
. An
interdependent association between species where they all benefit from each other or
compete for the same nutrients is expected.
1.2.3 Molecular biology techniques for unveiling microbes in tailings ponds
Although the characterization of microorganisms from the environment has been
traditionally done by cultivation in synthetic growth media, this retrieves only a small
fraction of species , estimated to be 0.1% or at most 10% of the total population 85
. This
is most likely because commonly used laboratory media do not adequately mimic the
environment in which most microorganisms grow. With the implementation of molecular
biology techniques, microbiologists are able to detect the uncultivated microbes that
make up a large fraction of the microscopic world. These techniques have allowed the
discovery of microbial species that for years remained unknown.
Specifically, small subunit ribosomal RNA (16S rRNA) gene-based analysis has
become a standard tool of molecular biology. This gene is an ideal marker biomolecule
because it is universal to cells, it is highly conserved structurally and functionally and it
is the central component of a complex translation apparatus in microbial cells. These
genes can be amplified using “universal” primers or primers specific for different groups
of microbes by the polymerase chain reaction (PCR). The PCR products can be further
separated by clone library construction, Denaturing Gradient Gel Electrophoresis
(DGGE), Single Strand Conformation Polymorphism (SSCP), Terminal Restriction
28
Fragment Length Polymorphism (TRFLP) or by pyrosequencing, among others. The
separated product can then be sequenced, identified and arranged into phylogenetic trees
that will help provide information on the possible role of these organisms in the
environment, usually by identification of the nearest cultivated relatives.
Some difficulties when determining microbial diversity in oil sand tailings could be
encountered, including the presence of microhabitats containing highly aggregating
bacteria in clumps or “hot spots” 86
. Hence, effective sampling is a key issue when
studying the microbial diversity in this type of ecosystem. Sometimes, the microbial
populations could be underestimated resulting in high variability between replicates 87
.
To target specific microorganisms based on function, specific primers are
constructed, narrowing their selection. This approach is very important in linking
community structure to activity. If these specific genes are detected, it is possible that the
metabolic process is taking place. Most recently, the emerging powerful method of
metagenomics or environmental genomics is capturing the attention of the scientific
community. The two primary goals of this approach are to identify the organisms present
in a sample by large scale sequencing and to identify what roles organisms have within a
specific environment. This is facilitated by 454 sequencing, a large-scale parallel
pyrosequencing system capable of producing billions of bases of sequences per day.
Overall, despite potential biases (such as low DNA yields 88
and the presence of
PCR inhibitors 89
, among others) molecular techniques are nowadays the most powerful
29
tool used to reveal organisms that are unable to grow in synthetic media that do
nevertheless play important roles in the biogeochemical cycles of Earth.
30
Chapter Two: Hypothesis and objectives
Oil sands tailings ponds represent an environmental concern to Alberta and
Canada. The large volumes of tailings that are generated daily, their high toxicity, and the
hazardous gases potentially emitted to the environment, pose a threat to the flora and
fauna in the area. In order to develop better tailings management strategies, it is
important to understand the physiology of microorganisms that grow in these niches. For
example, these microbes are the key players in sulfide and methane emissions but can
pontentially also be used to remediate toxins in tailings ponds. Thus, the monitoring of
these ponds over time would allow us to determine what microbes prevail and how they
correlate with the chemical parameters and microbial activity observed.
It was hypothesized that changes to tailings pond management operations shift the
pond microbial communities and activities, due to changes in selective pressures (e.g.
available electron acceptors or donors) to which the microbial communities are exposed.
For example, it is predicted that the addition of calcium sulfate (gypsum) or other
electron acceptors would inhibit methanogenesis, pond aging would result in the increase
of methanogen abundance and thus methanogenesis, and that pond closure (e.g., a
scenario where no new tailings or treaments are added to a tailings pond) will shift the
microbial community composition and activities (however, the outcome of pond closure
is not known - e.g. does pond closure lead to positive or negative effects?). Thus,
gaining information about the key microbial players and activities that occur in tailings
ponds subject to different management strategies can help operators predict whether
certain operations will lead to desired (e.g. biodegradation/bioremediation of tailings
31
chemicals) or undesired effects (e.g. gas emissions). The present research was thus aimed
to study the physiology of two tailings ponds to gain insight into the key microbial
processes and communities present. The ponds under study included an active pond
(pond 6) and an inactive pond (pond 5) which we were able to monitor just before and
after closure.
Specifically, the five major objectives of this thesis work were to:
1. Assess the microbial diversity in tailings ponds to determine the predominant
communities as a function of depth (Chapter 4)
2. Assess the key physiological processes in tailings ponds (sulfate reduction,
methanogenesis, sulfide oxidation) that can impact pond emissions and correlate these
with the microbial community findings (Chapter 4)
3. Quantify the major microbes responsible for sulfate reduction, methanogenesis
and sulfide oxidation in tailings using optimized qPCR analyses (Chapter 6)
4. Identify key electron donors (bitumen, naphtha, and naphthenic acids) that can be
used by the endogenous anaerobic and aerobic microbial communities (Chapters 5 & 7)
5. Test for the use of nitrate as an alternate electron acceptor to control
methanogenesis in tailings ponds and assess its impact on microbial community
composition (Chapter 7)
32
Chapter Three: Methods and Materials
3.1 Sampling and origin of oil sands tailings samples
The tailings samples used in this work were collected by Suncor Energy Inc. and
were collected as a function of depth. The samples were collected in autoclaved sterile
Nalgene bottles, filled to capacity, and tightly sealed to prevent oxygen contamination.
The samples were shipped to the laboratory by plane shortly after sampling. Upon
arrival, the bottles were kept in an anaerobic glove bag (COY Laboratory products Inc.)
containing an atmosphere of 90% N2 and 10% CO2. Subsamples of these were frozen at –
80 C in sterile, plastic 50 mL tubes for molecular studies. The rest remained in the
anaerobic hood for chemical analysis and to prevent oxygen contamination. This research
comprises the study of 4 years of monitoring (2008 – 2011) from 2 different ponds: Pond
5 (closed in 2010) [Table 3-1], and Pond 6 (active) [Table 3-2]. Tailings from both ponds
5 and 6 have been managed with the CT technology where MFT is combined with coarse
sand and gypsum slurry to form a non-segregating material that releases water allowing a
faster tailings consolidation.
Pond 5 is the first production-scale CT pond in the oil sands industry. It has been in
use since 1995 and extends about 3 km north south and about 5 km east west occupying
an area of approximately 15 km2 52
. After 12 years of tailings discharge, the pond reached
its capacity (deeper than 50 mbs) and was decommissioned at the end of the year 2009 52
.
Pond 6 started filling in 2002 and in the spring of 2010 had already reached its
capacity. At this time, the pond stopped receiving fresh tailings. Only CT tailings were
33
transferred into this pond. Therefore the pond has been considered “somewhat” active
since 2010. It has an approximate depth of 41 mbs and it is capped with 1 m of water
(personal communication, Dipo Omotoso, Suncor).
34
Table 3-1 Suncor Pond 5 sample information
Sampling
Date
GPS coordinates for samples Site
designation
Depths sampled (mbs)
June 2009
(before
closure)
57 0.4317N -111
32.46336W
P5S19A 1.8, , 2.4, 3.0, 4.6, 6.1,
7.6, 9.1, 10.7, 12.2, 13.7,
15.2, 19.8, 25.0, 29.0
July 2010
(after closure)
57 0.4317N -111
32.46336W
P5S19A 3, 6, 9, 12, 15, 18, 21, 24,
27, 30, 33, 36, 39, 42, 45,
48, 51, 54, 57, 60, 63
Table 3-2 Suncor Pond 6 sample information
Sampling
Date
GPS coordinates for samples Site
designation
Depths sampled (mbs)
October 2008 57 1.24812N -111 33.2466W
423 m
away from
P6S72A
0, 2, 3, 5, 6, 8, 9, 11, 12,
14, 15, 17, 18
June 2010 57 1.47426N -111
33.18378W P6S72A 3, 6, 9, 12, 15, 18, 21, 22
July 2011 57 1.47426N -111
33.18378W P6S72A
0, 3.5, 4, 7, 10, 13, 16,
18.5
35
3.2 Chemical techniques
3.2.1 Dissolved hydrogen sulfide concentrations in tailings
3.2.1.1 Preparation of reagents
Prior to sampling tailings samples a solution of DMPD (N, N-dimethyl-p-
phylendiamine-dihydrochloride) was prepared as follows: 1.0 g of DMPD and 1.0 g of
Zn(CH3COO)·2H2O were dissolved in 50 mL of concentrated H2SO4 together with 950
mL of ddH2O. This solution was dispensed (4.9 mL) in 15 mL test tubes followed by the
addition of 5.0 mL of ddH2O. A ferric chloride solution was prepared by mixing 5.0 g of
FeCl3 · 6H2O in deionized water to a final volume of 20 mL. Standards of 0.5 to 15.0 µg
of HS- were prepared from a stock solution of Na2S · 9H2O at 1000 mg · L-1
in anoxic
0.01 N NaOH.
3.2.1.2 Assay procedure
This assay was always prioritized so as to prevent sulfide loss and it is based on the
assay developed by Cline (1969) 90
. Therefore, it was done within the first 24 hours
following tailings samples arrival when the bottles were first opened in the anaerobic
bag. In the glove bag, approximately 10 mL of tailings were poured out from the
sampling jars and transferred to 15 mL sterile centrifuge polypropylene tubes. The tubes
were tightly capped and taken out of the anaerobic glove bag for centrifugation (1200 x
g, 10 min, IEC Centra GP8R). The resulting supernatant (tailings water) was collected
very carefully (100 µL) avoiding particles of oil and/or sand with a micropipette
(GILSON
- pipetman
) and rapidly transferred into the test tube with DMPD and water
36
described above. Immediately after, 100 µL of the ferric solution were added. Tubes
were vortexed and incubated at room temperature for 10 min to allow for color
development and absorbance was read on a spectrophotometer at 660 nm against a blank
90. When sulfide was present, the solution turned from light pink to blue. All
spectroscopic measurements were taken using a UV-1800 UV-VIS spectrophotometer
(Shimadzu). Sulfide concentrations were calculated based on the standard curve
obtained.
3.2.2 Dissolved hydrogen sulfide assay method for SOB experiments
Sulfide determination for SOB experiments described in section 5.2.1 were done
using the copper sulfide method 91
.
3.2.2.1 Preparation of reagents
A solution of zinc acetate (24 g of Zn(CH3COO)2 , 1.0 mL of 20% (w/w)
CH3COOH, dH2O adjusted to 1.0 L); 1.0 L of diamine reagent (2.0 g of 4-amino-N,N-
dimethylaniline, 600 mL of dH2O, 200 mL of concentrated H2SO4); and 100 mL of iron
alum solution (10.0 g of NH4Fe(SO4)2 ∙ 12 H2O, 2.0 mL of concentrated H2SO4, and
dH2O to complete 100 mL) were prepared.
3.2.2.2 Assay procedure
The samples (1.0 mL) from serum bottle experiments were obtained with a syringe
and centrifuged for 30 sec (maximum speed, Eppendorf) and 125 µL of the supernatant
were transferred into 25 mL vial that contained 2.0 mL of the zinc acetate solution.
Distilled water (8.5 mL) and diamine reagent (2.5 mL) were swirled with the sample and
37
the zinc acetate and a brick-red-orange color was allowed to develop. Immediately after,
125 µL of iron alum solution was added and the mixture was vortexed and allowed to
stand for 7 to 10 min at room temperature. In the presence of HS- the mixture turned to a
blue color. The mixture was adjusted to a final volume of 20 mL and OD was measured
spectrophotometrically against a blank at 670 nm.
3.2.3 Anion concentrations (nitrate, sulfate, and acetate) concentrations by HPLC
The water phase obtained from the centrifugation step described in section 3.2.1.2
was also used for sulfate and acetate determination 92
. For some depths, the water content
was not sufficient, thus more tailings sample was needed for centrifugation. The
supernatants were then filtered using a 0.2 µm membrane filter (VWR). The filtrate was
transferred into a clean 1.5 mL autosampler vial and then subjected to High Pressure
Liquid Chromatography (HPLC) in a Dionex ICS-5000 system. Samples were loaded
into an auto-sampler that used 25 µL of the sample for injection into the column. The
anions were separated on a 4 x 250 mm column (IonPac
AS18, Dionex) with a mobile
phase of water at a flow rate of 1 mL · min-1
(ICS-5000, Dionex). Standards were
prepared at 100, 200, 300, 400, and 500 µM from a 1 mM anion stock solution (SO42-
,
NO3-, NO2
-, Cl
-, acetate). Nitrate and sulfate concentrations in laboratory experiments
were prepared and analyzed in the same manner.
3.2.4 Water content
The water content in all tailings samples was measured following the ASTM
standard 93
. A known weight of tailings was dried in an oven at a temperature of 60 +/ 5
38
ºC to a constant mass. The water loss was calculated using the mass of water and the
mass of the dry specimen [Equation 1]. Duplicates of approximately 20 g of each tailings
sample were analyzed.
Equation 1 Water content
W = Mw/Ms x 100 (expressed in %) where: Mw: mass of water
Ms: mass of oven dry specimen
3.3 Microbial activity measuremets
3.3.1 Sulfate reduction rates (SRR)
Sulfate reduction rates were determined for all samples collected at all depths using
a method similar to that described by Ulrich et al. (1997) 94
.
3.3.1.1 Preparation of reagents
Anaerobic concentrated HCl
Concentrated hydrochloric acid (HCl) was placed in a serum bottle, leaving a
reasonable head space, capped and crimped followed by a continual flushing with N2 gas
for several minutes in the fume hood to make the acid anoxic.
Zinc acetate solution (10 %)
Boiled distilled H2O ( 100 mL) was bubbled with a flow of N2 and allowed to
cool. Zinc acetate (Zn(C2H3O2)2 (10 g) was added and once dissolved, the solution was
39
distributed in non-sterile serum bottles using a pipette. The bottles were capped and
crimped and stored in the anaerobic hood.
Chromium – acid solution (Cr(III)-HCl)
A solution of Cr(II) (1 M) was prepared in HCl (0.5 N) in a volumetric flask.
Separately, one third of a glass bottle was filled with mossy Zn and washed several times
with HCl (0.5 N). Then the Cr/HCl solution was added to the mossy Zn and bubbled for
15 to 20 min with N2 gas. After this time, the Cr solution turned color from green to
crystal blue due to the reduction of Cr(III) to Cr(II). The solution was distributed using a
glass pipette into serum bottles previously flushed (with N2), capped and crimped.
Labelled sodium sulfate (35
SO4) stock solution
A stock solution of 10 µCi· mL-1
of 35
SO42-
was prepared in distilled anaerobic H2O
from a stock solution of 1 mCi · mL-1
(Perkin-Elmer). The volume was enough to add 1
mL of radioisotope per serum bottle of 10 mL to have a final concentration of
approximately 1.0 µCi· mL-1
in each experiment.
3.3.1.2 SRR technique
In the anaerobic glove bag, samples of tailings (5.0 g) were distributed into 60 mL
serum bottles and capped with rubber stoppers. Then 5.0 mL of anoxic, autoclaved water
was added with a syringe resulting in a total volume of approximately 10 mL. At this
point, the sulfate concentration of the diluted tailings was determined by using HPLC
[section 3.2.3]. For this determination, 300 µL of tailings were taken using a previously
40
flushed syringe. The diluted tailings were shaken and 1 mL of the radioisotope stock
solution was added using a 1 mL syringe. Samples (100 µL) for each serum bottle were
taken for counts per minute (cpm). This value represents the initial concentration of
35SO4
2-. The samples were incubated in a shaker in the fume hood for 5 to 7 days. After
the incubation time, 8 mL of tailings were transferred into clean anaerobic serum bottles
that contained a 2.5 mL 10 % zinc acetate solution [Figure 3-1].
The samples were then acidified with 4.0 mL of Cr(II)-HCl and 4.0 mL of
concentrated HCl. The mixture was incubated for 3 d on a slow shaker to allow the H2S
to be converted into its gaseous state and trapped in the zinc acetate traps. The amount of
35S-sulfide collected in the zinc acetate trap (along with the remaining
35S-sulfate in the
tailings to ensure mass balance) was quantified by liquid scintillation counting on a
BECKMAN LS6500. The SRR was calculated using Equation 2 94
and expressed in nmol
SO42- · cm
-3 · day-1
. Samples from each depth and sampling event were subjected to this
technique.
Equation 2 SRR calculation
where: SRR: Sulfate Reduction Rate
SO42-
]: Sulfate conc. in tailings (nmol · cm-3
)
35
S-H2S: cpm in the sulfide trap
35
S-SO42-
: cpm in tailings
t: Incubation time (days)
: discrimination factor for 35
S (1.06)
[SO42-] x (H2
35S) x
(35SO42-) x t
SRR =
41
Figure 3-1 Schematic representation of the zinc acetate trap for SRR determination.
Tailings are incubated with the 35
SO42-
for 5 to 7 days, then the tailings are acidified
with a mixture of Cr(II)-HCl and the resulting H2 35
S generated is trapped in the
zinc acetate solution previously introduced into the bottle. The cpm in the sulfide
trap is counted in scintillation equipment to determine how much of the original
sulfate was reduced to sulfide.
42
3.3.2 Methanogenesis rates
3.3.2.1 Sample preparation
For samples collected from each depth, 20 mL of tailings were transferred into
sterile, anoxic 60 mL serum bottles, capped and crimped. Some samples were autoclaved
to create sterile controls. Samples were incubated at room temperature in the dark.
Methane concentrations were determined in the headspace at day 0, day 12, and after 36
d of incubation. Rates were calculated based on methane produced after first 36 days in
nmol CH4 · cm-3
tailings ·day-1
.
3.3.2.2 Methane measurements by gas chromatography
Methane formation over time was monitored to determine rates in tailings samples
and in enrichment cultures (different carbon sources and nitrate experiments) using a gas
chromatograph (GC) 95
. Using a sterile syringe, preflushed with N2/CO2 (90/10), 0.2 mL
of the incubation headspace was sampled and injected into a HP model 5890 GC
equipped with a flame ionization detector maintained at 200 °C. Injections were carried
out at 150 °C onto a packed stainless steel column (6 ft. 9 1/8 in., Poropak R, 80/100,
Supelco) held isothermally at 100 °C. Methane amounts were determined based on
calibration curves prepared from standards containing known methane concentrations.
43
3.4 Microbial community composition
3.4.1 DNA Extraction
For tailings samples, approximately 500 mg of sample from each depth was used
for DNA extraction using the Fast DNA Spin Kit for Soil (MP Biomedicals) according to
the manufacture’s protocols. For samples collected from Pond 6 2008 only, the DNA was
extracted using the same procedure plus skim milk powder (Fluka analytical) (40 mg · g
of tailings -1
) to enhance DNA recovery from tailings
96.
For the water samples (surface water), 1 mL of sample was taken and DNA was
extracted using Fast DNA Spin Kit (MP Biomedicals).
For laboratory enrichment cultures, 1 mL of culture fluid was typically sampled
and DNA was also extracted using the FastDNA Spin kit (MP Biomedicals).
3.4.2 16S r DNA Pyrosequencing
The extracted DNA (typically 2 ng·µL-1
) was subjected to polymerase chain
reaction (PCR) amplification of 16S rRNA genes using 12.5 μL of 2xPCR Master Mix
(Fermentas), 10.5 μL of nuclease-free water (Fermentas), 1 μL of genomic DNA (2 ng),
and 0.5 μL of FLX Titanium amplicon primers 454TRA and 454T-FB (20 pmol μL-1
) for
a 25 μL PCR reaction. These have the sequences for 16S primers 926f (aaa ctY aaaKga
att gac gg) and 1392r (acg ggc ggt gtg tRc) as their 3′- ends. Primer 454T - RA has a 25
nt A-adaptor (CGTATCGCCTCCCTCGCGCCATCAG), whereas primer 454T-FB has a
25 nt B-adaptor sequence (CTATGCGCCTTGCCAGCCCGCTCAG).
44
Following PCR amplification (95 °C, 3 min; 25 cycles of 95 °C 30 s, 55 °C 45 s, 72
°C 90 s; 72 °C 10 min; final hold at 4 °C) with primers 454T-RA and 454T-FB, the PCR
product was verified on a 0.7% agarose gel and purified with a QIAquick PCR
Purification Kit (Qiagen).
For tailings samples where the concentration of the PCR product obtained was too
low (< 5 ng · µL) or the presence of primer dimers appeared in the gel, a touch down
PCR protocol was used. This protocol was as follows: 1 cycle of 95°C for 5 min for
denaturation; 30 cycles of 30 s at 95°C, 30 s at 60°C, decreasing 0.5°C/cycle, and 30 s at
72°C. Then another 30 cycles of 30 s at 95°C, 30 s at 55°C and 30 s at 72°C were carried
out. Finally, the last cycle was for 10 min at 72°C. This protocol was used with
individual PCR reagents from Qiagen.
PCR product concentrations were determined on a Qubit Fluorometer (Invitrogen),
using a Quant-iT dsDNA HS Assay Kit (Invitrogen). PCR products (typically 20 μL of
20 ng·μL-1
) were sent to the Genome Quebec and McGill University Innovation Centre,
where they were subjected to 10 PCR cycles with primers 454T-RA-X and 454TFB,
where X is a 10 nt multiplex identifier barcode. The barcoded PCR products were
analyzed by pyrosequencing, using a GS FLX Titanium Series Kit XLR70 (Roche
Diagnostics Corporation). DNA from skim milk powder was extracted and amplified
with the same protocol as used for the tailings pond samples in order to determine the
organisms associated with this reagent.
45
3.4.3 Analysis of pyrosequencing data
The pyrosequencing data were analyzed by the Phoenix 2 pipeline 97
. Sequences
with low-quality reads and potential chimeras were removed. The sequences thus filtered
were used to generate operational taxonomic units (OTUs) based on consensus sequences
of clusters obtained with differences of 3% and 5 % between them (clustering distance
cut-offs). The OTUs were assigned taxonomically based on the SILVA 108 data set
Small Subunit rRNA Database Release 108 (SSU Ref NR 108; http://www.arb-
silva.de/no_cache/download/archive/release_108/Exports), a highly curated database for
phylogenetic analysis.
The resulting reads at the phylum and genus levels were analyzed by selecting the
most abundant OTUs with a cut-off of 3 % (e.g. those taxa that were present at > 3%
abundance in the whole community). For environmental samples (tailings from ponds 5
and 6), the 3% cut-off was applied to the percent of pyrosequencing OTUs for each depth
and to the average percent of pyrosequencing OTUs (except for the TPW samples where
the average percent of pyrosequencing OTUs was not considered). For the enrichments,
the 3 % cut-off was used based on the % of pyrosequencing OTUs of each particular
experiment.
The taxonomic analysis was carried out at the phylum level to detect the microbial
distribution at a high level, considering that some of the DNA sequences were not always
assigned to a particular genus. However, for all the samples, the genus level was also
46
assessed because more detailed information (e.g. presumed microbial function) can be
obtained at this level, thus allowing a better interpretation of our results.
Biodiversity studies were also carried out by the evaluation of the species richness
and evenness distribution within each sample analyzed. Two types of biodiversity were
evaluated (alpha and beta). The alpha diversity refers to diversity within a particular
sample, and the beta diversity measures the diversity of several samples within a habitat.
Within these types of diversities, biodiversity indices were considered such as the
Shannon index, which measures evenness of the species in the community 98
; and the
Simpson index, which focuses on dominance of species 99
. For the Shannon index, the
higher the value obtained, the greater the number of taxa (higher biodiversity) and the
more evenly they are distributed. The lower the Simpson index (the closer to zero)
indicate that less diversity is found in a community as there is a dominance of some taxa
over others for a particular sample. At the same time, the Chao index was also evaluated
as this indicated the estimated total number of OTUs obtained 100
. Rarefaction curves and
Non-Metric Muldimensional Scaling (NMDS) were also plotted which allowed us to
visualize the microbial community richness and the relationship between the samples,
respectively. The rarefaction curve plots the number of OTUs found as a function of the
number of samples (# of reads). Therefore it generates the expected number of OTUs in a
small subset of samples (# of reads) drawn at random from a large pool of samples (reads
or sequences) 101
. Thus, a rich community would have a curve that initially has a steep
slope but levels off as fewer new taxa are found per additional number of sequences
analyzed, indicating that a reasonably sufficient number of samples were collected from
47
the environment. On the other hand, if the curves level off very quickly (at low number
of samples (# of reads)), fewer taxa are obtained, this is an indication of saturation as
fewer taxa are present. 101
. The NMDS plot shows grouping of closely related samples
together within a two-dimensional space, whereas less closely related ones will be shown
sparsely (farther apart from one another) in the space. Relational trees were also
generated using the Bray-Curtis dissimilarity calculation which describes the
dissimilarity between the structures of two communities
(http://www.mothur.org/wiki/Braycurtis).
An overview of all of the samples processed for microbial community analysis and
activity and enrichment studies from ponds 5 and 6 is shown in Table 3-3.
3.5 Microbial laboratory enrichments
The Dutchman Martinus Beijerinck (1851 – 1931) first proposed the enrichment
culture technique. He proved that when providing specific nutrients to a natural sample,
the growth of microorganisms with certain physiological properties can be promoted in a
very selective way 54
. For this aspect of the research, enrichments of aerobic and
anaerobic microorganisms were accomplished with the aim of studying particular
microbial behaviour activity with selected carbon substrates including bitumen, NAs, and
naphtha.
48
Table 3-3 General overview of all tailings samples used for microbial community
analysis by 454 pyrosequencing and for the various experiments described in this
thesis.
Pond Year
sampled Experiment / microbial community analysis
Pond 5 2009 natural environment - Sulfide oxidation
tests
- NA isolates
2010 natural environment Nitrate enrichments
Pond 6 2008 natural environment
(DNA extracted with
skim milk powder)
Quantitative PCR
(DNA extracted with skim
milk powder)
2010 natural environment Quantitative PCR
(DNA extracted with skim
milk powder)
Anaerobic carbon
source enrichments
2011 natural environment Quantitative PCR
(DNA extracted with skim
milk powder)
49
3.5.1 Incubation Media
A variety of different media were used to establish aerobic and anaerobic
enrichments [shown in Tables 3-4 to 3-10].
3.5.2 Aerobic enrichments on naphthenic acids
One litre of TPW from Suncor Energy Inc. pond 5 (sampled on September 1, 2009)
was filtered using a 0.2 µm filter to collect cells. Then the filter was soaked in a 50 mL
sterile saline solution (0.85 % NaCl in water (w/v)) to allow the bacteria to detach from
the filter into the saline solution. The cell suspension was used as the microbial inoculum
by growing it in a basal salt medium (Bushnell-Haas, MBH medium) 72
described in
Table 3-4 supplemented with the selected model NAs.
One percent inoculum from the original saline solution with the filter was added to
50 mL of MBH containing 100 mg·L-1 of a model NA. Cyclohexanecarboxylic acid,
cyclohexaneacetic acid, cyclohexanebutyric acid, cyclohexanepropionic acid,
cyclohexanepentanoic acid (all from Aldrich®),
were each prepared as a basic solution
(0.1 N NaOH) at a concentration of 6.0 g · L-1 that was used as the substrate stock
solution (1.0 mL added to 50 mL medium). The inoculated flasks were incubated at room
temperature for 28 d and growth was monitored using a UV 1800 spectrophotometer (at
OD of 600 nm, Shimadzu).
Several transfers of these initial incubations were done (1% of inoculum) before
isolating single cells in the solidified MBH medium (same as above but with 1.5% agar)
50
supplemented with its corresponding NA. Morphologically distinct colonies were
isolated as pure cultures and a subset of each was identified by their 16S rRNA gene
sequence after PCR amplification. More specific details about the isolates are described
in Section 5.2.3.
Inocula for NA time course biodegradation experiments were prepared in lysogenic
broth (LB) [Table 3-5] to obtain a high density of cells. The cells were washed with
MBH medium and then transferred to the MBH medium amended with the particular
model NA.
3.5.3 Aerobic medium for sulfide oxidation assays
For the sulfide oxidation assays, CSB-A medium [Table 3-6] was prepared and
autoclaved in a Widdel flask. While the medium was still hot, 1 mL of trace elements
[Table 3-9], 1 mL of selenite tungstate, 30 mL of 1 M NaHCO3, and 3 mL of 1 M Na2S
were added. The pH was adjusted to 7.0. The medium was dispensed (60 mL) in 120 mL
serum bottles sealed with rubber stoppers. Tailings from each depth (3 mL, refer to
section 5.2.1) were added to the medium in the anaerobic hood. The sulfide concentration
was measured using the copper sulfide method 91
[section 3.2.2] and adjusted when
needed to 3 mM.
3.5.4 Anaerobic enrichments
For anaerobic enrichments, Pfennig medium 102
was used [Table 3-7, Table 3-8,
and Table 3-9].
51
To prepare this medium, all the ingredients were mixed except for the sodium
bicarbonate (NaHCO3), and the pH was adjusted to 7.1 to 7.3. The medium was boiled to
eliminate any oxygen followed by a bubbling of N2/CO2. NaHCO3 was added to the
medium once cooled, then the medium was distributed in flushed N2/CO2 serum bottles.
Appropriate amounts of a 2.5 % solution of cysteine sulfide, (0.1 mL per 100 mL for
nitrate-reducers, 2 mL per 100 mL for sulfate-reducers and methanogens), was added to
each sealed bottle to serve as a reductant. Cysteine sulfide was prepared by dissolving 5.0
g of cysteine-HCl and 5.0 g of sodium sulfide in NaOH (0.1 N) under anoxic conditions.
Details on each particular experimental set up are described under the Methods section of
each chapter.
52
Table 3-4 Modified Bushnell - Haas salt (MBH) medium composition.
Component g/L water
KH2PO4 1.0
Na2HPO4 1.0
NH4NO3 0.5
(NH4)2SO4 0.5
MgSO4 · 7H2O 0.2
CaCl2 · 2H2O 0.02
FeCl3 0.002
MnSO4 · 2H2O 0.002
Table 3-5 LB (lysogenic broth) medium
Component g/L water
Tryptone 10.0
Yeast extract 5.0
Sodium chloride 5.0
Table 3-6 CSB-A medium composition.
Component g/L water
NaCl 7.0
KH2PO4 0.2
MgCl2 6H2O 0.4
KCl 0.5
CaCl2 2H2O 0.15
NH4Cl 0.25
Resazurin (0.1 %) 2 to 3 drops
53
Table 3-7 General anaerobic medium composition
Component Amount / 100 mL water
Pfennig I 5 mL
Pfennig II 5 mL
Wolin metals 1 mL
Balch vitamins 1 mL
Resazurin 0.1 mL (of a 0.1% solution)
NaHCO3 0.35 g
(+/- electron acceptor)
(+/- substrate)
Table 3-8 Pfennig solutions
Component g per Litre
Pfennig I
K2HPO4 10.0
Pfennig II
K2HPO4 10.0
MgCl2 6H2O 6.6
NaCl 8.0
NH4Cl 8.0
CaCl2 2H2O 1.0
54
Table 3-9 Wolin trace metal solution
Component g per Litre
EDTA 0.5
MgSO4 3.0
MnSO4.H2O 0.5
NaCl 1.0
CaCl2.2H2O 0.1
ZnSO4.7H2O 0.1
FeSO4.7H2O 0.1
CuSO4.5H2O 0.01
Na2MoO4.2H2O 0.01
H3BO3 0.01
Na2SeO4 0.005
NiCl2.6H2O 0.003
Table 3-10 Balch vitamin solution
Component mg per Litre
biotin 2.0
folic acid 2.0
pyridoxine-HCl 10.0
thiamine-HCl 5.0
riboflavin 5.0
nicotinic acid 5.0
DL calcium pantothenate 5.0
vitamin B12 0.1
PABA 5.0
lipoic acid 5.0
mercaptoethane- sulfonic acid (MESA) 5.0
55
Chapter Four: Microbial physiology and communities in oil sands tailings ponds
4.1 Introduction
To characterize the microbial community composition and physiology in tailings,
two ponds from Suncor Energy Inc. were studied over the years 2008 to 2011. Pond 6, an
active pond, and pond 5, a pond that was initially active but was closed after a few years
of continuous tailings discharge, (shown in Figure 4-1) were studied. Both ponds are
located in Suncor’s Lease 86/17 area (north of Fort McMurray, AB).
Suncor Energy Inc. is committed to a program of closure and reclamation of ponds
5 and 6 which have been receiving products from the oil sands mining operations since
the mid 1990s – early 2000s, respectively. Pond 6 is currently capped with water and
MFT are being withdrawn for the TRO treatment whereas pond 5 is being dewatered and
capped with coke. The latter is scheduled for completion in 2019 52
. These reclamation
strategies have the final goal of decreasing the consolidation time of the MFT layers,
therefore accelerating the landscape recovery times.
Ponds 5 and 6 have undergone the CT treatment where gypsum is continuously
added to enhance densification rates of the tailings and around 90% of the water is
recycled back into the extraction plant. Under current bitumen extraction technology,
Suncor Energy Inc. uses naphtha as the organic solvent that helps in the bitumen
detachment from the sand particles therefore the froth tailings discharged into the ponds
contain some naphtha components.
56
As overviewed in this chapter, a depth dependent profile throughout the anaerobic
zone (starting at the mud line) of each pond was analyzed from a chemical and
microbiological point of view to have a better insight into the geochemical cycles
currently ongoing and the microbial contribution to each. Finally, the effect of pond
closure in pond 5 is discussed as a positive outcome of Suncor Energy Inc. tailings
management operations.
A portion of this work (overviewing findings from Pond 6 2008 samples) was
previously published in Environmental Science and Technology 55
.
57
Figure 4-1 Aerial view of Suncor ponds 5 and 6. Image courtesy of Suncor Energy
Inc.
Pond 5
Pond 6
58
4.2 Methods in brief
4.2.1 Pond 6 (active pond)
Our laboratory received samples from pond 6 over three years (2008, 2010, and
2011) from the coordinates listed in section 3.1, Table 3-2. The samples herein analyzed
were taken from below the mud line, ranging from 3 to 18 mbs. Below 20 mbs, the MFT
is highly consolidated, thus no samples could be taken. Samples were stored
anaerobically or frozen and analyzed for a variety of chemical parameters, water content,
microbial community composition, and microbial activities as described in sections 3.2,
3.3, and 3.4.
4.2.2 Pond 5 (inactive pond)
During the year 2009 and 2010, we evaluated the chemical parameters (sulfate,
sulfide) together with anaerobic microbial activity (sulfate reduction and methanogenesis
rates) to assess the effectiveness of the closure of pond 5. Samples were taken
immediately after closure (2009) and a year after (2010). Sample coordinates are listed in
section 3.1, Table 3-1. Samples were analyzed for a variety of chemical parameters,
water content, microbial community composition and microbial activities as described in
sections 3.2, 3.3, and 3.4.
59
4.3 Pond 6, an active tailings pond
Samples from tailings pond 6 from Suncor Energy Inc. were used for the microbial
molecular and physiology studies of an active pond. The pond started filling in 2002 and
in 2010 had already reached maximum capacity. It has an approximate depth of 41 m
below the mud line, and it is capped with about 1 m of water. The pond is currently
considered a somewhat active pond in that no fresh tailings are currently being
incorporated into the pond but MFT is continuously drawn from pond 6 for MFT drying
(Suncor’s Tailings Reduction Operation). In the year 2011 some MFT from pond 2/3
were transferred to pond 6 (a one-time activity), which is an active pond that receives
fresh froth tailings therefore it is rich in naphtha [Figure 4-2].
The pH of pond 6 ranges from 7.0 to 7.8 and the average temperature is about 20
C year round. Only the surface water freezes during the winter months but underneath
this layer the temperature remains stable at around 15 to 18 C 37
.
Pond 6 generally has no visible gas emissions except during the winter months,
when occasional gas accumulated under the iced water cap can escape to the atmosphere
when punctured (Suncor Energy Inc. personal communication).
60
Figure 4-2 Flow diagram of Pond 6 management activities during the years 2008 to
2011. Based on personal communication with Suncor Energy Inc.
61
4.3.1 Results
4.3.1.1 Microbial community composition in pond 6
Phylum level analysis
The microbial community in pond 6 at the phylum level did not vary much from
2008 to 2011 [Figure 4-3 (A)]. The most abundant phylum present was Euryarchaeota.
This group, which mainly included methanogens 54
, was found in 2008 and 2011 to
comprise approximately 40% average of the pyrosequencing OTUs but in 2010 this
phylum almost doubled in abundance [Figure 4-3(A)]. The next most abundant phylum
was Proteobacteria. This group is considered the largest and most metabolically diverse
of all Bacteria 54
. It comprises a wide diversity of chemolithotrophic,
chemoorganotrophic, and phototrophic species 54
. The proportions of pyrosequencing
OTUs for Proteobacteria are very similar during the years 2008 and 2011, around 40%
each, with relatively lower in abundance for the 2010 samples. Members of other phyla
like Chloroflexi and Firmicutes were also detected in all the years sampled, but in
fractions no higher than 10% of the average of pyrosequencing OTUs [Figure 4-3(A)].
Genus level analysis
At the genus level, pond 6 exhibited a diverse but constant microbial population
during the three-year period studied [Figure 4-3(B)]. However, samples from 2008
showed a higher diversity of pyrosequencing OTUs (> 3% abundance) when compared
with samples from 2010 and 2011 [Figure 4-4 (A)]. The extracted DNA from these
tailings were dominated by methanogens, primarily by members of the acetotrophic
62
Methanosaeta genus. In particular, Methanosaeta is by far the most abundant
methanogen genus in all the samples collected from pond 6 [Figure 4-3(B), Figure 4-4
(A, B, C)]. It was found disseminated throughout the pond but occasionally peaking in
abundance towards the shallower depths [Figure 4-4 and Figure 4-5 (A)]. In addition,
many other genera were present at > 3% of the total community abundance. These
included other methanogens, Methanolinea and Methanosarcina, Syntrophus (a known
syntroph), the S and Fe cycling bacterium Thiobacillus, the SRB Desulfocapsa, and
several putative hydrocarbon-degrading bacteria (Pseudomonas, Acinetobacter,
Acidovorax).
In the year 2010, Methanosaeta sp. were the most abundant at the genus level,
reaching values ranging from 20 to 40% with no particular distribution pattern. For this
same year a substantial reduction of Syntrophus sp. (decreased abundance from 3% to 0)
and a 5-fold increase in Methanosarcina abundance was observed [Figure 4-3 (B)]. The
second most abundant methanogen was Methanolinea [Figure 4-3 (B, C)]. This genus
was found in all the tailings depths but in higher proportions in the upper mud line region
(above 6 mbs) [Figure 4-5 (A)]. Other methanogens were also detected but in relatively
low abundance, with the exception of Methanosarcina that was more abundant in
samples collected in 2010 [Figure 4-5 (A)]. Syntrophus comprised the third most
abundant genus for pond 6 [Figure 4-3 (C)]. The most prominent sequences at the genus
level that are involved in sulfate reduction metabolism are affiliated with Desulfocapsa.
For pond 6, SRB were always found in lower abundance than methanogens (less than 10
% of pyrosequencing OTUs), especially when the sulfate became limited. Desulfocapsa
63
sp. were found in all depths but mainly at the top, around 3 mbs, middle sections (12
mbs) or at the bottom, below 15 mbs [Figure 4-5 (B)]. Other genera like Acinetobacter
and Pseudomonas also inhabited the pond but to a lesser extent. Acinetobacter was
mainly present in 2010 and 2011, but Pseudomonas were found in all three years
sampled [Figure 4-3 and Figure 4-4]. Other phyla refers to an average of 25 phyla
whereas other genera refers to approximately 150 genera [Figure 4-3and Figure 4-4]For
more information regarding the most abundant total microbial community members
detected in all years sampled, refer to Appendix One:.
64
Figure 4-3 Most common microbial members found in Suncor pond 6 tailings at (A)
phylum level, (B) genus level, and (C) total average of most common genera in the
three years sampled. The selection was based on the average of the most common
taxa for the three years sampled. Other genera and/or phyla refer to average % of
pyrosequencing OTUs present at lower than 3% abundance in the total community.
0 20 40 60 80 100
2008
2010
2011
Average % of pyrosequencing OTUs
year
sam
pled
Euryarchaeota
Proteobacteria
Chloroflexi
Firmicutes
other phyla
0 20 40 60 80 100
2008
2010
2011
Average % of pyrosequencing OTUs
year
sam
pled
Methanosaeta
Methanolinea
Syntrophus
Acinetobacter
Pseudomonas
Methanosarcina
Desulfocapsa
other genera
24.49
4.202.85
2.64
2.072.00
1.89
59.85
Methanosaeta
Methanolinea
Syntrophus
Acinetobacter
Pseudomonas
Methanosarcina
Desulfocapsa
other genera
A
B
C
65
Figure 4-4 Depth dependent profile of most abundant percentage of pyrosequencing
OTUs in pond 6 at the genus level (A) in 2008, (B) in 2010, and (C) in 2011. Notice
that pond 6 samples collected in 2008 have the highest abundance of genera
comprising > 3 % of the community.
0
5
10
15
20
25
0 10 20 30 40 50 60
Dep
th (
mbs
)
% of pyrosequencing OTUs
Methanosaeta
Methanosarcina
Pseudomonas
Methanolinea
Acinetobacter
0
5
10
15
20
25
0 10 20 30 40 50 60
Dep
th (
mbs
)
% of pyrosequencing OTUs
Methanosaeta
Acinetobacter
Syntrophus
Methanolinea
Desulfocapsa
0
5
10
15
20
25
0 10 20 30 40 50 60
Dep
th (
mbs
)
% of pyrosequencing OTUs Methanosaeta
Methanolinea
Syntrophus
Desulfocapsa
Leptolinea
Smithella
Thauera
Thiobacillus
Brachymonas
Acidovorax
A
B
C
66
Figure 4-5 Distribution of selected microbial community composition at the genus
level (as % of pyrosequencing OTUs) found in Suncor pond 6 sampled in 2008,
2010, and 2011 as a function of depth. (A) Methanogens and syntrophs:
Methanosaeta (■), Methanolinea (೦), Syntrophus (▲), Methanosarcina (); (B) sulfur
metabolism, mainly Desulfocapsa (∆) as dominant SRB.
Methanogens and syntrophs
0
5
10
15
20
25
0 20 40 60
% of pyrosequencing OTUs
0
5
10
15
20
25
0 20 40 60
Dep
th (
mb
s)
0
5
10
15
20
25
0 20 40 60
2008 2010 2011
0
5
10
15
20
25
0 2 4 6 8
Dep
th (
mb
s)
0
5
10
15
20
25
0 2 4 6 8
% of pyrosequencing OTUs
Sulfur metabolism
A
B
0
5
10
15
20
25
0 2 4 6 8
67
4.3.1.2 Relationship between pond 6 samples
From a microbial community point of view, pond 6 showed a relatively constant
diversity throughout the years. The Shannon and Simpson indices for this pond suggest
there is a somewhat diverse community (relatively high Shannon indices) with some
dominance of some taxa over the other (Simpson’s values closer to zero) [Appendix
Five: Table 0-6], mainly dominated by Methanosaeta sp. [Figure 4-3 (B)]. The numbers
of samples studied as a whole seem to have been enough to taxonomically characterize
pond 6, as the rarefraction curves slightly turned into the saturation limit towards the end
of the curve, we could assume reasonable coverage of the major communities [Appendix
Six: Figure 0-1]. All samples taken in 2010 clustered together in the phylogenetic tree
and that cluster was separate from the 2011 samples that also clustered together [Figure
4-6], which confirms the non-relateness between these two sampling periods. However,
samples from 2008 seem to be more similar to 2011 as some of the depths from 2008
samples (from 3 to 9 mbs) are clustered with the 2011 samples [Figure 4-6]. The rest of
2008 samples are either not directly related to any of the sampling years (2010, 2011) or
closely related to pond 6 2010 (2 mbs). NMDS analysis [Figure 4-7] shows that the
microbial communities in samples collected at different times generally clustered
together.
68
Figure 4-6 Relational tree clustering for pond 6 samples (2008, 2010, 2011). Bray-
Curtis dissimilarity was used to calculate the distance.
69
Figure 4-7 NMDS diagram showing all oil sands tailings samples collected from
pond 6 in 2008 (●), 2010 (♦), and 2011 (■).
70
4.3.1.3 Microbial activity and chemistry of the pond
Over time, Suncor pond 6 showed a decrease in sulfate and sulfide concentrations
[Figure 4-8(A, B)]. The sulfate concentration at the surface was highest above the mud
line (shallower than 3 mbs) of the pond, especially in the 2008 samples where a
maximum of 6 mM was measured. However, in 2011, sulfate levels decreased to around
1 mM in the surface water layer. Below the mud line, the highest sulfate values were
always observed at deeper depths, below 14 mbs [Figure 4-8(A)]. The same was true for
SRR where the maximum activities were measured either near the top of the anaerobic
zone (near the mud line) or deep below the mud line. A marked average SRR decrease
from 10.8 nmol·cm-3·d-1
in 2008 to nearly zero in 2010- 2011 was observed [Figure
4-8(D), Table 4-1]. Average sulfide concentrations also decreased from 2008 (~ 3 mM)
to 2010-2011 (~ 0.4 mM). While the pond remained active (2008), the sulfide
concentrations were relatively high throughout the depths. However, as the pond became
less active (2010-2011), the highest concentrations of sulfide were found to be more
towards the shallower depths of the pond, within the first 10 meters below the surface
[Figure 4-8(B)].
Methane production had an average rate above 30 nmol·cm-3·d-1
for the years 2008
and 2011, however a four fold decrease was measured for the 2010 samples [Figure
4-8(C), Table 4-1]. For all the years sampled the highest methanogenesis rates were
found fluctuating at depths shallower than 15 mbs [Figure 4-8 (C)]. The acetate
concentrations also fluctuated but peaked at discrete depths above 15 mbs [Figure 4-8
(E)], particularly in 2010, where the highest acetate concentrations were detected at 3
71
mbs (~ 7.5 mM), and at 15 mbs (~ 6 mM) [Figure 4-8(E)]. The average acetate
concentration found ranged between 0.065 to 1.8 mM over the sampled years. Overall,
pond 6 had the highest activity between the mud line and 15 mbs which matches with the
highest water content in the pond [Figure 4-8 (F)].
72
Figure 4-8 Chemistry and microbial activity in pond 6 determined during the years
2008 (♦), 2010 (೦) and 2011 (∆). Depth dependent profiles of: (A) sulfate
concentrations; (B) sulfide concentrations; (C) methanogenesis rate; (D) sulfate
reduction rate; (E) acetate concentrations; and (F) water content (no water content
measurement was performed for 2008 samples).
0
5
10
15
20
25
0 2 4 6 8
Dep
th (
mbs
)
Sulfate (mM)
0
5
10
15
20
25
0 20 40 60 80 100
Dep
th (
mbs
)
CH4 rate (nmol . cm-3 . d-1)
0
5
10
15
20
25
0 20 40 60 80 100
SRR (nmol . cm-3 . d-1)
A B
C D
0
5
10
15
20
25
0 2 4 6 8Sulfide (mM)
0
5
10
15
20
25
0 2 4 6 8
Dep
th (
mbs
)
Acetate (mM)E
0
5
10
15
20
25
0 50 100 150
Water Content (%) F
73
Table 4-1 Average SRR, methanogenesis rates, and putative methane evolution
prevented in various samples collected over time in pond 6.
Sampling year
Average SRR
(nmol·cm-3·day
-1)
Average CH4
production
(nmol·cm-3·day
-1)
CH4 prevented (%)
2008 10.8 37.3 22.4
2010 0.4 9.0 3.9
2011 0.1 34.0 0.2
74
4.4 Effect of pond closure: Pond 5, an inactive pond.
Suncor’s pond 5 is the first consolidated tailings pond being reclaimed in Alberta’s
oil sands region. It was decommissioned in December 2009 and it is being reclaimed in a
three- phase period [Figure 4-9]. The first phase (2009 – 2012) involves the capping
process, which is currently in its final season of construction. The second phase (2012 –
2019) includes drilling of wick drains into the pond through the coke cover to facilitate
the in-situ dewatering operations. The third phase, which is planned for 2019, is the final
land form and establishment of regional flora and fauna. An aerial view of how the pond
looks in 2012 is shown in Figure 4-10.
Every year, this pond is monitored as a function of depth to determine the change
in the physicochemical parameters over time and to evaluate the effectiveness of pond
reclamation. Starting in 2009, we have received subsamples from different depths for
microbial-based studies. This section describes the microbial community analysis and
physiological studies carried out on samples recovered just after closing and
approximately one year later.
75
Figure 4-9 Concept of Pond 5 reclamation strategy. (Courtesy of Suncor Energy
Inc.).
76
Figure 4-10 Views of pond 5 with geofabric and coke covering. (Image courtesy of
Suncor Energy Inc.)
77
4.4.1 Results
4.4.1.1 Microbial community composition before and after pond 5 closure
Phylum level analysis
The average percentages of pyrosequencing OTUs at the phylum level are shown in
[Figure 4-11(A)]. During the years 2009 and 2010, a high proportion of the average %
OTUs belonged to Proteobacteria, comprising approximately 70% of the community
OTUs. Second in abundance were Euryarchaeota. In 2009, members of this phylum
reached an abundance of 26% while in 2010, a 12% abundance was observed. Other
phyla like Chloroflexi and Firmicutes sequences were also present but at a lower
percentage of pyrosequencing OTUs. Significantly, Firmicutes were more abundant in
the samples taken in 2010, comprising 4.5% of OTUs [Figure 4-11(A)]. A year after
pond closure (2010 samples) a slight increase in the abundance of sequences affiliating
with the Proteobacteria was observed (up to 77%) while a decrease of the ones grouped
under Euryarchaeota (to 12%) was observed. Other phyla refers to an average of 17 phyla
[Figure 4-11(A)].
Genus level analysis
At the genus level, a marked difference in the relative abundance of organisms
between the two sampling times was evident, shown in Figure 4-11(B). At the genus
level, samples from 2009 were more dominated by the methanogen Methanosaeta, an
acetate-using methanogen, whereas in samples from 2010, Pseudomonas sp., appeared to
dominate the community identified [Figure 4-11(B)]. Other genera referes to
approximately 99 genera in 2009 and 200 genera in 2010 [Figure 4-11(B)].
78
Figure 4-11 Average of pyrosequencing OTUs in pond 5 in 2009 and 2010 . (A)
Phylum level, (B) Genus level. Other genera and/or phyla refer to average % of
pyrosequencing OTUs lower than 3% of the total abundance of OTUs.
A
B
0 20 40 60 80 100
2009
2010
Average % of pyrosequencing OTUs
Yea
r sa
mp
led
Proteobacteria
Euryarchaeota
Chloroflexi
Firmicutes
other phyla
0 20 40 60 80 100
2009
2010
Average % of pyrosequencing OTUs
Yea
r sa
mp
led
Pseudomonas
Acidovorax
Methanosaeta
Acinetobacter
Desulfuromonas
Methanolinea
Thiobacillus
Brachymonas
other genera
79
In 2009, Methanosaeta was found throughout the depths but was more abundant
towards the shallower areas. For example, at 6 and 7 mbs, approximately 28% of
pyrosequencing OTUs aligned with Methanosaeta. However, deeper into the pond, the
abundance decreased to below 12 % [Figure 4-12(A)]. Although Methanosaeta was also
present after the pond was closed, its abundance decreased reaching its maximum
percentage at 3 and 18 mbs with 17 and 28 % of pyrosequencing OTUs, respectively
[Figure 4-12(B)]. Another group affiliating within the Archaea that was present in
relatively high abundance (average 3.9%) before the closure of the pond in the shallower
depths was Methanolinea, a H2/CO2-using methanogen [Figure 4-11(B)]. However, in
2010, this genus decreased in abundance to less than 3% [Figure 4-11(B)]. Similarly,
other genera like Thiobacillus, Brachymonas, and Thauera were relatively abundant
before pond closure [Figure 4-11(A)] but scarcely found in 2010 with the exception of
Thauera [Figure 4-11(B)]. Acidovorax and Comamonas were present in both years but at
a higher abundance after pond closure [Figure 4-11(B)]. Specifically, at 51 mbs,
Acidovorax reached its highest abundance, comprising 48% of the pyrosequencing reads
[Figure 4-12(B)]. Rhodoferax was found in pond 5 in samples from 2009 at %
pyrosequencing OTUs higher than 3%, but was only detected in samples from 2010 at a
less than 3% abundance.
In summary, members of the genus Pseudomonas increased in abundance from 1.6
% in 2009 to 35 % in 2010, and Acidovorax increased 5 times in 2010 compared with the
average % found in 2009. On the other hand, the abundance of Methanosaeta decreased
from 15.4 % to 7 % [Figure 4-11(B)]. For more information regarding the microbial
community composition detected in pond 5 please refer to Appendix Three:.
80
Figure 4-12 Depth dependent profile of most abundant OTUs (> 3% of the total
community OTUs) in pond 5 at the genus level (A) in 2009 before pond closure, (B)
in 2010 after pond closure.
0
5
10
15
20
25
30
35
0 20 40 60 80
Dep
th (
mb
s)
% of pyrosequencing OTUs
Methanosaeta
Thiobacillus
Brachymonas
Methanolinea
Thauera
Rhodoferax
Pseudomonas
A
B
0
10
20
30
40
50
60
0 20 40 60 80
Dep
th (
mb
s)
% of pyrosequencing OTUs
Pseudomonas
Acidovorax
Methanosaeta
Acinetobacter
Desulfuromonas
Comamonas
Thauera
Methanolinea
81
4.4.1.2 Microbial relationship between the two sampling periods (before and after pond
closure)
Both sampling times showed a somewhat diverse community composition,
although samples from 2009 were richer according to higher values of Shannon indices
[Appendix Seven: Table 0-7]. However, the low Simpson indices (closer to zero) inferred
dominance of some taxa over others, which most likely refers to Methanosaeta in 2009
and Pseudomonas in 2010. The differences in their microbial composition due to a shift
from a community dominated by methanogens to one dominated by putative
hydrocarbon-degraders, make both sampling times very different. This was confirmed by
the phylogenetic tree construction and NMDS plots where the communities from each
sampling year grouped together in two separate clusters [Figure 4-13 and Figure 4-14].
The results are confident as the rarefaction curves showed curve lines reaching a plateau
towards the end of the curve confirming that sufficient samples were taken from each
period [Appendix Eight: Figure 0-2].
82
Figure 4-13 Relational tree clustering for pond 5 samples (2009, 2010). Bray-Curtis
dissimilarity was used to calculate the distance.
83
Figure 4-14 NMDS plot of the two sampling times in pond 5 to illustrate their
statistical compositional difference. (●) pond 5 2009, (♦) pond 5 2010.
84
4.4.1.3 Sulfate-reducing and methanogenic activity in pond 5 before and after closure
Sulfate concentrations measured in tailings samples from pond 5 (2009 – 2010)
were fairly low (0 - 0.5 mM) for the majority of the depths sampled, except near the
surface of the pond (3 mbs). At this depth, samples collected in 2010 showed an increase
in sulfate concentration compared with 2009. A maximum of 4.2 mM was observed in
2010 compared to 1.6 mM of sulfate initially detected in 2009 [Figure 4-15(A)]. Since
sampling in 2010 was carried out deeper in the pond, high values of sulfate were also
measured at increasing depths, averaging 1.5 mM. However, at these depths, no
comparison can be made as no samples were received below 29 mbs in 2009 [Figure
4-15 (A)].
Sulfide concentrations in the pond were very low (almost zero) at both sampling
times. But, similar to sulfate, the highest values of sulfide were found close to the surface
of the pond (3 mbs). However, in contrast to sulfate, the sulfide values at 3 mbs
decreased from 1.1 mM in 2009 to 0.07 in 2010 [Figure 4-15(B)].
The sulfate and sulfide profiles correlated with the microbial activity, as
determined by methanogenesis rates and SRR in tailings shown in Figure 4-15 (C, D).
The average methanogenesis rate decreased from 5.6 to 0.07 nmol CH4·cm-3
tailings·d-1
and SRR decreased from 16.6 nmol·cm-3
tailings·d-1
in 2009 to 3.5 nmol·cm-3
tailings·d-1
in 2010.
85
The microbial activity measurements also showed that the highest activities in the
pond were found towards the surface (in the upper 10 mbs), corresponding to higher
water content values [Figure 4-15(E)].
Although methanogenesis activity was not prevalent at deeper depths, there
appeared to be a deep pocket of sulfate-reducing activity between approximately 50 – 60
mbs as measured in the 2010 samples [Figure 4-15 (D)], which correlated with the higher
sulfate concentrations measured at this depth [Figure 4-15 (A)].
86
Figure 4-15 Chemical characterization and microbial activity measurements of
pond 5 before pond closure in 2009 (♦) and after pond closure in 2010 (೦). (A)
Sulfate concentrations, (B) Sulfide concentrations, (C) Methane production rate, (D)
Sulfate reduction rate, and (E) Water content. The error bars represent the
standard error of two replicates.
0
10
20
30
40
50
60
70
0 2 4 6 8
Dep
th (
mb
s)
Sulfate Concentration (mM)
0
10
20
30
40
50
60
70
0 2 4 6 8
Sulfide Concentration (mM)
0
10
20
30
40
50
60
70
0 20 40 60 80 100
Dep
th (
m)
CH4 rate (nmol ·cm3 ·d-1)
0
10
20
30
40
50
60
70
0 20 40 60 80 100
SRR (nmol cm3 ·d-1)
0
10
20
30
40
50
60
70
0 50 100 150
Dep
th (
mb
s)
Water content (%)
A B
C D
E
87
4.5 Discussion
4.5.1 Physiological and chemical characterization of an active pond
Understanding how microbial communities behave in tailings ponds is a
challenging task but is necessary in order to obtain baseline information and develop
tools to direct current and future management strategies. Microbes enriched in the ponds
can affect the tailings fate in many different ways. They can contribute to increased or
decreased densification rates 15,44,45
; they can be very detrimental to the environment by
producing harmful gases 45
, or they can convert complex hydrocarbon compounds into
less toxic substances 81
.
In order to study the microbial community composition in an active pond, and to
assess the correlation between these populations and the microbial physiology and
chemistry in the tailings, a series of oil sands tailings samples from pond 6 as a function
of depth were studied [Table 3-2]. It should be pointed out that since our microbial
community survey was PCR-based, it likely suffered from PCR biases even though the
primers used were designed to amplify a wide range of Bacteria and Archaea 103
. Hence,
the survey presented here has its limitations. In addition, the DNA extraction protocol
used for 2008 samples was carried out using skim milk powder which enhances the DNA
detachment from clay particles therefore increasing the DNA recovery from our samples
96. This could be the reason why samples from 2008 were more diverse than samples
from 2010 and 2011[ Figure 4-4], and that not all the samples within the year 2008
clustered together in the phylogenetic tree [Figure 4-6] or NMDS graph [Figure 4-7]. No
skim milk powder was used for samples from 2010 and 2011.
88
In general, the microbial analysis (community structure and physiological
experiments) as a function of depth confirms that there are at least two major metabolic
processes currently ongoing in the tailings ponds: methanogenesis and sulfate reduction.
Figure 4-16 shows a schematic diagram of the dominant processes ocurring in pond 6
(based on the work reported here), along with the changes in microbial community
composition over time for pond 6. For each sampling year, many of the same taxa are
present, however, the relative abundance of the taxa changed. The occurrence in time and
space in the abundance of one taxa over another appears to depend on the availability of
electron acceptors, fluidity of tailings, and management of the pond (e.g., fresh tailings
input).
Overall, based on the three years sampled (2008, 2010, and 2011), microbial
community analysis revealed that pond 6 is heavily colonized by methanogens, in
particular Methanosaeta [Figure 4-4]. Penner and Foght 40
previously reported the
dominance of Methanosaeta in two Syncrude tailings deposit samples (MLSB) indicating
that acetoclastic methanogenesis could be the primary route for methane production in
tailings ponds 40
. Methanogens are a unique group of anaerobic organisms that conserve
energy during the production of methane. In general, they are capable of using specific
compounds such as hydrogen, acetate, methanol, and methylated compounds but may
also rely on symbiotic cooperation with other bacteria for energy from other carbon
sources 104
. This type of cooperation, known as syntrophy, enables both organisms to
energetically depend on each other to degrade complex substrates 105
.
89
Figure 4-16 A schematic of the dominant microbial processes found in Suncor’s oil
sands tailings pond 6 based on data obtained in this work. Changes in the average
relative abundances of the key microbial taxa over time are indicated on the right of
each figure.
0
22
Dep
th (
mbs
)
oxic zone
Anoxic zone
CH4
HS-HC
Small MW
compounds,
H2, acetate,
H2S SO42-/S8
H2,
CO2SO4
2-
Putative HC degraders: Pseudomonas (4.0%),
Acinetobacter (2.5%)
SRB: Desulfocapsa (0.7%)
Syntrophs: Syntrophus (0.7%)
Methanogens: Methanosaeta (36%),
Methanosarcina (5.9%),
Methanolinea (3.9%)
2010
0
22
Dep
th (
mbs
)
oxic zone
Anoxic zone
CH4
HS-HC
Small MW
compounds,
H2, acetate,
H2S SO42-/S8
H2,
CO2SO4
2-
Putative HC degraders: Acidovorax (1.4%)
SRB: Desulfocapsa (2.8%)
Syntrophs: Syntrophus (3.3%), Smithella (2.4%)
Methanogens: Methanosaeta (19.5%),
Methanolinea (4.6%)
2008 Active pond
0
22
Dep
th (
mbs
)
oxic zone
Anoxic zone
CH4
HS-HC
Small MW
compounds,
H2, acetate,
H2S SO42-/S8
H2,
CO2SO4
2-
Putative HC degraders: Acinetobacter (5.4%)
SRB: Desulfocapsa (2.2%)
Syntrophs: Syntrophus (4.5%)
Methanogens: Methanosaeta (18%),
Methanolinea (4.2%)
2011
Pond capped with water
MFT inputs from pond 2/3
MFT withdrawn for drying technology
90
Indeed, the observation that Syntrophus (a syntroph thought to be involved in
methanogenic hydrocarbon metabolism 106
) was among the most abundant bacterial
genera in pond 6 aligns with the idea of syntrophy [Figure 4-3 and Figure 4-4]. In
enrichments with MFT from Syncrude Canada Inc. amended with naphtha, the presence
of both Methanosaeta and Syntrophus was observed 68,69
. The association of species
belonging to these genera suggests their participation in n-alkane and/or BTEX
biodegradation in MFT 68,69
.
Members belonging to the genus Methanosaeta are obligate anaerobes and extreme
metabolic specialists that use acetate as the sole source of energy and acetate as the sole
carbon sources with concomitant production of CH4 107
. The methyl carbon of acetate is
reduced to methane while the carboxyl carbon is oxidized to CO2 108
. The persistence of
these kinds of methanogens in the pond may be due to the ability of most of the
Methanosaeta species to grow in strong bundles of aggregated filaments 107
, and to their
coupling mechanisms with syntrophs to degrade complex organic compounds in different
environments 69,109-112
. The low levels of acetate (usually less than 0.5 mM) in tailings
also supports their growth due to their high affinity and low threshold for this organic
compound 112,113
[Figure 4-8 (E)].
The increase in relative abundance of methanogens from 2008 to 2010 was not
surprising as it was previously suggested that with age, tailings ponds have a tendency to
become methanogenic 44
. The pond was already 8 years old in 2010 when it had reached
maximum capacity and the input of fresh tailings into the pond ceased. This implied that
no more SO42-
was available for SRB, as gypsum was no longer added; resulting in a
91
microbial population shift towards the methanogenic Archaea in the anaerobic zone 44,110
.
However, it is not clear why a decrease in methane production rates was observed in
2010 [Figure 4-8 (C), Table 4-1]. However, one explation may be attributed to the
increase in acetate concentration to above 4 mM [Figure 4-8 (E)]. The high
concentrations of acetate could be inhibiting the dominant Methanosaeta sp. (who prefer
acetate concentrations to be less than 1 mM), while enhancing Methanosarcina sp., that
proliferate at higher acetate concentrations 104,109
[Figure 4-4 and Figure 4-5]. However,
Methanosarcina sp. may not be present in the pond at high enough abundance to support
methanogenesis at rates similar to that observed in 2008. In addition, a reduction in the
abundance of Syntrophus sp. was also observed in samples from 2010 [Figure 4-3 (B)],
suggesting that methanogenic activity decreased due to lower abundance of syntrophic
partners able to utilize other carbon sources. Therefore, although the pond was closed in
2010, no more gypsum was added, and the % of methanogenic archaea increased, these
organisms may not have been as active at the time of sampling. Interestingly, in 2011, the
relative abundance of methanogens was similar to the year 2008. It was in this year
(2011), that the pond was disturbed due to the implementation of the TRO technology.
The disturbance included extracting MFT from pond 6, which probably accounted for
oxygen incorporation into the pond with the concomitant inhibition of methanogens
therefore resulting in decreased abundance in 2011 with respect to 2010 [Figure 4-3(A)].
Simultaneously, more gypsum-treated tailings from ponds 2/3 was added to pond 6
[Figure 4-2]. These fresh tailings inputs may be responsible for the increased
methanogenic activity as more microbes (methanogens and syntrophs) were added to the
pond. Figure 4-3 (B) supports this idea as the patterns for microbial distribution at the
92
genus level in 2008 and 2011 are very similar, with the exception of Acinetobacter sp., a
putative hydrocarbon degrader 114
, that increased its abundance from 0 to 5.4 % of
average OTUs [Figure 4-3(B) and Figure 4-4(B, C)]. This could be due to the pond
enrichment with naphtha coming from ponds 2/3.
The second most common organism found in all samples from pond 6 (with the
exception of samples from 2010), is the strict anaerobe, H2- or formate-utilizing
methanogen, Methanolinea. Species of this genus tend to grow in multicellular filaments,
a very suitable morphological feature to enhance the nutrient uptake in CT ponds which
could be somewhat challenging 54,115
. Based on our results, Methanolinea also seems to
be closely metabolically coupled to Syntrophus as they showed a similar spatial
distribution in the pond [Figure 4-5(A)]. As previously mentioned, Syntrophus can
metabolize a wide variety of organic compounds including for example, benzoate and
hexadecane 71,116,117
. Hence, a proposed cooperative mechanism in the ponds could be
described in Equation 3 71
using hexadecane as a model hydrocarbon. The decomposition
of hexadecane by Syntrophus leads to the formation of hydrogen and acetate [Equation
3(a)] that is then cleaved into CH4 and CO2 for instance by Methanosaeta sp. [Equation 3
(b)]. Finally Methanolinea can then metabolize CO2 and H2 into more CH4 [Equation
3(c)] 71
.
93
Equation 3 Decomposition of hexadecane to methane by three groups of organisms
The spatial distribution of Syntrophus and Methanolinea mirrors the
methanogenesis rate observed in pond 6 where the highest activity was mainly found
towards the upper layers of the pond, near the mud line [Figure 4-8(C)]. Therefore,
despite their low abundance with respect to Methanosaeta, the microbial activity
suggests that Methanolinea sp. also plays an important role in methane production in the
pond.
The relative abundance of SRB decreased over time as sulfate became less
available due to pond closure. SRR assays confirmed this, as notable differences from
2008 to 2010 and 2011 were perceived [Figure 4-8(D)]. Sequences phylogenetically
affiliated with the sulfur disproportionating bacterium Desulfocapsa seem to be the
leading group of sulfate reducers in tailings pond 6 [Figure 4-5(B)]. Their abundance
throughout the pond suggests that they can either be disproportionating oxidized
inorganic sulfur intermediates such as thiosulfate and sulfite or carrying out the
conventional sulfate reduction. Species of Desulfocapsa have been found to be
metabolically diverse. For instance, D. thiozymogenes is able to grow as a sulfate reducer
4 C16H34 + 64 H2O 32 CH3COO- + 32 H+ + 68 H2 ∆G = - 929 kJ
32 CH3COO- + 32 H+ 32 CH4 + 32 CO2 ∆G = - 385 kJ
68 H2 + 17 CO2 17 CH4 + 34 H2O ∆G = - 282 kJ
(a)
(b)
(c)
94
on short chain alcohols while while D. sulfexigens cannot reduce sulfate despite having
the complete enzyme machinery 118,119
.
The origin of the high concentration of sulfate at the surface is not known, but
some speculation can be made as an explanation. It is known that methane bubbles
generated at lower depths of the pond can rise to the surface, scavenging particles,
surface active materials, bacteria, and even oil, creating an important vertical transport
mechanism 60
. Hydrogen sulfide produced by SRB at deeper depths for instance, could be
partitioning with methane bubbles being transported to the surface where it can be
oxidized back to sulfate either chemically or biologically. In fact, the neutral pH of
tailings favor the presence of hydrogen sulfide as HS- which has a tendency to precipitate
as iron and other metal sulfides 16
, therefore little sulfide will escape to the surface as gas.
Further work to provide evidence to support this speculation is presented in Chapter
Five:. Another explanation for the high sulfate concentrations at the surface could be that
the sulfate added originally accumulates as more TPW is recycled and this remains in the
surface water (e.g. as a dissolved solute) as no SRB activity typically occurs in aerobic
environments.
Considering that 1 kg of gypsum per cubic meter of tailings is added to the pond,
approximately 7 mM of sulfate would be expected to remain in the tailings if no SRB
were carrying out sulfate reduction 3. Interestingly, most of the sulfate was found to be
consumed within the tailing pond 6, but at depths below 18 mbs, higher sulfate levels
were measured [Figure 4-8(A)]. This could have different explanations: (i) as tailings
consolidate, less water is available, therefore a reduction in the microbial activity
95
including the reduction of sulfate is expected; and (ii) at these depths, carbon sources are
limited due to depletion of biodegradable compounds, leaving “untouched” the
recalcitrant complexes, and as a result, lower sulfate reduction occurs. This together with
the disproportionation of incompletely oxidized sulfur compounds (e.g., by Thiobacillus
sp.) may explain some pockets of higher sulfate in the deeper zones. These pockets could
also be the result of ground water filtration into tailings ponds, but this has not been
proven so far.
As was previously suggested by Salloum et al. (2002) 16
, the addition of gypsum to
tailings contributes to a decrease in methanogenesis. Because the reduction of CO2 to
methane and the reduction of sulfate to sulfide both require 8 electrons, sulfate reduction
by SRB will prevent the formation of an equivalent amount of methane. Thus, based on
the SRR and methanogenesis rates observed in pond 6, we were able to estimate the
approximate percent of theoretical methane that was not released to the environment due
to the availability of sulfate [Table 4-1]. As the pond aged, however, less sulfate was
available and therefore more methane could potentially evolve from the pond.
In conclusion, if maintained undisturbed, pond 6 has a high risk of becoming more
methanogenic and methane bubbles may eventually be released from the pond. The
microbial composition observed as well as the microbial activity measured indicated that
such a pattern trend was occuring from 2008 to 2011. However, current management
strategy being followed by Suncor Energy Inc., where MFT is being removed from this
pond for the drying technology, could likely contribute to decreasing these risks.
96
4.5.2 Effect of pond closure
In an effort to lower the environmental impacts produced by oil sands mining
operations, and to comply with the eco-friendly rules and directives enforced by the
ERCB, Suncor Energy Inc. has started to engage in new tailings management strategies.
In this regard, pond closure and the TRO technology are leading the way in the
Athabasca area.
After a year of closure, pond 5 is already showing the positive outcomes of this
management approach. Our results revealed that at the time of closure (2009), the
microbial community present in the tailings pond was mainly methanogenic. Thus, high
potential risks for methane release into the atmosphere would have been expected if no
actions were taken. At that time, the most abundant organisms found were members of
the genus Methanosaeta. Similar to what was found in pond 6 [section 4.3.1.1], species
grouped under this genus are dominant in tailings ponds. The substrate availability
(acetate), pH range and temperature, favors their development 40,111,120,121
.
Interestingly, following a whole year of zero input of fresh tailings and dewatering
of the pond, there was a shift in the microbial community from one dominated by
methanogens (Methanosaeta sp.) to one dominated by putative hydrocarbon-degraders
(Pseudomonas sp.) [Figure 4-11(B)]. This shift may have different explanations: (1)
water stress to endogenous microorganisms due to pond dewatering, (2) toxicity and/ or
bioavailability of carbon sources to methanogens as only the less biodegradable
compounds are left, and (3) presence of oxygen in the pond due to Suncor’s operation
disturbances.
97
In the process of pond closure, water is at times being removed from the pond 52
.
Operators have the final goal of a completely dewatered pond before the final capping is
approved. Hence, only microbes that have a high tolerance to water stress may survive
successfully under these circumstances. Such is the case of Pseudomonas species, a well-
known genus of bacteria with the ability to survive under high water stress environments.
Pseudomonas can be widely found in nature, as they are very well adapted to harsh
conditions. In pond 5, sequences affiliating with Pseudomonas can be found throughout
the pond, even at depths were water was less available [Figure 4-12(B)]. Their cell wall
characteristics, as well as their ability to grow in a biofilm structure, make them very
resistant to high toxicity and desiccation conditions. In vitro studies of direct culturing of
oil sands tailings microbes showed Pseudomonas species as the predominant biofilm
producer 38
. This capability for cell aggregation is mainly due to the production of
extracellular polymeric substances (EPS) which are biosynthetic polymers of high
molecular weight such as polysaccharides, proteins, nucleic acids, phospholipids; along
with non-polymeric constituents of low molecular weight. These extracellular
compounds are found surrounding the cells and are also key in the formation of flocs,
sludges and biogranules 122
. This protective matrix can hold several times the microbe’s
weight in water thereby allowing the diffusion of nutrients to the cell wall 123
. In addition,
some strains of Pseudomonas aeruginosa are known to produce lipases,stable enzymes
under water restriction conditions that allow these bacteria to survive in low water
environments 124,125
. Likewise, production of biosurfactants by Pseudomonas sp. seems
to help in their survival when water is very low by regulating the hydraulic potential
gradients 123
. Microscopy analysis of tailings by scanning electron microscopy (SEM)
98
has revealed the presence of microbial aggregates and the presence of EPS 15
. This
suggests that microbial cells with such characteristics in tailings could potentially be
bounded to clay particles with the concomitant formation of clay hutches. This feature is
also thought to be contributing to tailings sedimentation over time 15
.
In contrast to Pseudomonas sp., some methanogens are very sensitive to water
stress 126
and oxic environments and could die after exposure to any of these .
Nonetheless, there are methanogenic strains that have developed the ability to adjust and
survive when long periods of complete dehydration or oxygen exposure is an issue. Such
is the case of methanogens in wetland rice based cropping systems where cycles of
flooding and drainage occur 127
. However, we do not think such is the case for tailings
methanogenic organisms since the methanogenic community in the pond is not adjusted
to these water stress cycles. Therefore, either water stress or oxygen incursion due to the
introduction of the dewatering wicks into the pond may be a key point regarding a
decrease in the methanogenic population 52
. Nevertheless, the continued presence of
Methanosaeta sp. under these conditions may occur because they have the ability to form
aggregates which in the long term protect them from extreme conditions such as water
and oxygen stress .
Finally, the availability of organic compounds (e.g. carbon sources) in tailings
becomes challenging for some microbes. In contrast, Pseudomonas are known to degrade
a wide range of hydrocarbon compounds which under these conditions, especially if
oxygen is available, could be very favorable. Furthermore, the ability of Pseudomonas to
produce surfactants may allow them to have access to more complex compounds 128
.
99
The lack of nutrients together with low water content (less than 20 vol %) may also
explain the presence of sulfate pockets at deeper layers in the pond (below 50 mbs). As
explained earlier, these factors could be affecting the SRR [Figure 4-15 (A, D)],
contributing to an increase in the sulfate concentrations in comparison with shallower
depths. The same pattern was observed in pond 6 (2010 samples) where below 21 mbs
the water content also reached values below 20 vol% [Figure 4-8(F)], and high sulfate
concentrations, compared with the rest of the anaerobic layers, were measured [Figure
4-8(A)].
In conjunction with Pseudomonas, other species could be playing important roles
in the biodegradation of hydrocarbons in tailings ponds. The persistence of Acidovorax
sp. both in 2009 and in 2010 suggests this. In particular, in 2010, Acidovorax sp.
increased in population from 2.4 to 10 % of the average pyrosequencing OTUs [Figure
4-11(B)]. Many hydrocarbon contaminated sites have previously shown Pseudomonas
and Acidovorax as dominant genera 114129
. These two together with Acinetobacter have
known hydrocarbon degrading ability 114
, including PAHs 130-134
. Furthermore
Acidovorax species may also be involved in the oxidation of iron coupled to nitrate
reduction 135
. Other genera with known denitrifying capabilities are Thauera 136
,
Brachymonas, and Comamonas 137
. All of them have also been previously found in
hydrocarbon contaminated environments 138-140
. Although no nitrate was detected in
tailings samples from pond 5, nitrite concentrations range from 1 to 2 mM (data not
shown). The Thiobacillus genus detected in samples from 2009 and Desulfuromonas
detected in 2010 samples, have members known to be involved in sulfur metabolism, and
100
may be carrying out this function in pond 5. The obligate chemolithotroph Thiobacillus
can oxidize iron sulfides (pyrite) while using nitrate as electron acceptor 141
. They have
been found to possess the enzyme sulfite cytochrome c oxydoreductase that oxidizes
sulfite and produces sulfate 142
. On the other hand, Desulfuromonas sp. apart from
degrading hydrocarbons, is a well-known iron- 114,143
and sulfur-reducer in anoxic
sediments 144
. Since species known to be associated with iron metabolism are being
detected in relatively high abundance in tailings, more research will need to be done in
this area to better understand other metabolic processes apart from methane production or
sulfate reduction in tailings ponds.
4.5.3 A comparison between active and inactive ponds
Comparing the two ponds studied we can conclude that each one is a unique
ecosystem in terms of spatial distribution and type of organisms found. The
phylogenetic relationship between the samples showed that pond 5 and 6 clustered
separately, but within each pond the the communities within a given sampling time tend
to be grouped together [Figure 4-17]. For example, although pond 6 was sulfate-reducing
and methanogenic initially (2008), it appears to have shifted to being mainly
methanogenic, with a prevalence of Methanosaeta and Methanolinea most likely coupled
with Syntrophus species. The inactive pond 5 also showed a change in the microbial
community composition within a year following pond closure, from being mainly
methanogenic (dominated by Methanosaeta), to a community dominated by putative
hydrocarbon-degraders such as Pseudomonas sp. and Acidovorax sp.
101
The microbial activity (e.g. rates of methanogenesis, SRR) for each pond generally
decreased over time presumably due to a reduction of tailings input, particularly for the
inactive pond. In pond 5, the anaerobic microbial activity was found close to the surface
of the pond whereas for the active pond (pond 6) the anaerobic microbial activity is more
homogeneously distributed throughout the depths sampled.
Unquestionably, tailings ponds harbour a wide variety of organisms that interact
among each other in complex microbiological cycles. The physiological and community
structure analysis carried out in these two ponds has given evidence of how tailings
management (e.g. inputs, or lack of inputs that alter chemistry) influences the microbial
population in these ecosystems. Thus, the strategy of dewatering and pond closing when
tailings ponds have become methanogenic is a good approach for achieving the directives
toward a safer environment in northern Alberta as our results suggest a community shift
away from predominantly methanogenic to favor alternate microbial activities.
102
Figure 4-17 NMDS of all tailings samples collected (pond 5 2009, 2010, and pond 6
2008, 2010, 2011) showing how samples collected in the same year cluster.
103
Chapter Five: Microbiology at the surface of tailings ponds
5.1 Introduction
Tailings pond surface water, also known as tailings process water (TPW) is part of
the post-process waste in the extraction of bitumen from the oil sands. As the tailings
solids settle in the ponds, the pore water rises and can be reused in the extraction process.
Although some chemical parameters may change due to the recycling of the water, in
general, TPW are moderately hard (15–25 mg · L-1 Ca
2+, 5–10 mg · L-1
Mg2+
) with a pH
(hydrogen ion concentration) of 8.0–8.4 and an alkalinity (a measure of the carbonate) of
~800–1000 mg · L-1 HCO3
-. TPW also contains dissolved solids including sodium (~500
to 700 mg · L-1), bicarbonate, chloride (~75 to 550 mg · L-1
), and sulfate (~200 to 300 mg
· L-1) and organic compounds such as bitumen, NAs, asphaltenes, BTEX, cresols, humic
and fulvic acids, phenols, phthalates, and PAHs 19
. Trace metals have also been detected
such as (in mg · L-1): aluminum (Al) (0.07 – 0.5), arsenic (As) (0.06 – 0.015), cadmium
(Cd), chromium (Cr) (0.003 – 2.0), copper (Cu) (0.02 – 0.9), iron (Fe) (0.8 – 3.0), lead
(Pb) (0.04 – 0.19), Nickel (Ni) (0.006 – 2.8), and zinc (Zn) (0.01 – 3.2) among others 19
.
The surface water of tailings ponds is most exposed to environmental changes.
During the winter months, just the surface water tends to freeze and in the summer, it
thaws completely allowing a more active microbial life. It has been speculated that three
important microbial processes occur in the surface water of tailings pond: (1) oxidation
of sulfide by sulfide-oxidizing bacteria (SOB) 62
, (2) naphthenic acid biodegradation
104
67,145,146, and (3) aerobic methane oxidation. In this chapter, only the first two processes
will be addressed.
As was previously suggested (section 4.5.1) H2S ions produced by SRB in the
anoxic zone of the pond, may be transported to the surface by CH4 bubbles 60
. Once the
bubbles reach the surface, they burst releasing the H2S , which is subsequently oxidized
to S8 (abiotically) or to SO42-
(biotically). To test this hypothesis, tailings waters and
tailings from different depths of pond 6 sampled in 2008, amended with sulfide and
exposed to air, were monitored for sulfide loss over time. Separately, surface water
samples from ponds 5 and 6 were microbiologically characterized by 454
pyrosequencing. The results of these experiments are described in this chapter.
Naphthenic acids (NAs) are thought to be one of the sources of toxicity in TPW 36
.
Their concentration ranges from 40 to 70 mg · L-1 but can occasionally reach as high as
130 mg · L-1 32
. They are present in tailings ponds because they are solubilized during the
hot caustic treatment used in the extraction of bitumen although they can also be the
result of incomplete biodegradation of bituminous compounds once in the pond 80
. One
of the most difficult challenges the oil sand industry faces today is the treatment of these
NA-containing waters before they can be discharged 19
. Thus, devising mechanisms to
eliminate or convert them into less toxic structures is of great interest to oil sands
operators. Microbial degradation could be one alternative, as NAs have been previously
proven to be biodegradable to some extent 31,34,65,67,81,82,145,147-150
. It is known from a
handful of previous studies that the oxidation of these compounds can occur by -
oxidation of the aliphatic side chain and that their biodegradability depends on the extent
105
of alkyl side chain branching 81,145,151
. However, the detailed metabolic pathways through
which biodegradation occurs have not been well described and it may vary depending on
the microbes. As also described in this chapter, aerobic enrichments to cultivate and
isolate bacterial NA degraders were established and a series of NA biodegradation
experiments with pure bacterial isolates were carried out.
5.2 Methods
5.2.1 Sulfide oxidation experiments
For sulfide oxidation tests, 3 mL of tailings from different depths of pond 6
sampled in 2008 were added to sterile serum bottles containing 60 mL of a mineral salts
medium (CSB-A medium, Table 3-6) amended with sodium sulfide (~3 mM starting
concentration) 95
. Experiments were initiated by adding 45 mL of air, and sulfide
concentrations were measured at time 0 and at 20 min intervals (up to 100 min) using the
copper sulfide method 91
(described in section 3.2.2). Controls included sterile sulfide-
containing medium and heat-killed tailings in sulfide-containing medium. Samples for all
determinations were prepared in the anaerobic glove bag.
5.2.2 DNA extraction and 454 pyrosequencing from tailings surface waters
Microbial community analysis of TPW was conducted using 454 pyrosequencing
following DNA extraction. DNA extraction of three water samples [Pond 6 2008, Pond 5
2009 (before pond closure), and Pond 6 2011, based on availability] were obtained using
the procedure described in section 3.4.1 and microbial community composition was
analyzed as described in section 3.4.3.
106
5.2.3 Isolation and identification of naphthenic acid-degrading bacterial isolates
Isolation and culturing of the isolates was described in section 3.5.2. The selected
isolates were subjected to DNA extraction using a DNA extraction kit (Fast DNA Spin
kit; MP Biomedicals) followed by PCR amplification of the 16S rRNA genes. The PCR
reaction contained 25.0 µL of 2 x PCR master mix (Fermentas), 21.0 µL of nuclease-free
water (Fermentas), 2.0 µL of extracted DNA and 1.0 µL of primers (27f/1392r) 152
for a
PCR reaction totalling 50 µL.
Amplified products were visualized on 1% agarose gels, purified (Qiagen) and
sequenced in both directions with the same primers used for the amplification (University
Core DNA Services, University of Calgary). Sequences derived from the forward and
reverse primers were manually aligned by overlapping the sequences, typically by ~100
bases. Putative identities were determined based on the nearest phylogenetic relative in
the BLASTn (NCBI; http://www.ncbi.nlm.nih.gov/blast; default settings) or RDP II
(Ribosomal Database Project II; http://rdp.cme.msu.edu; default settings) databases. The
RDP II database was used to corroborate the identification obtained in the BLASTn
searches.
5.2.4 NA biodegradation time course experiments
The inoculum used for the biodegradation experiment was prepared by growing the
isolates on LB broth (described in 3.5.1,Table 3-5). The cells were washed and
suspended in sterile saline solution until an approximate concentration of 1 x 108 cells ·
mL-1
was obtained (equivalent to the 0.5 tube on the MacFarland scale). To obtain a 1 %
107
inoculum in the biodegradation experiment, an aliquot from this suspension was then
inoculated into Erlenmeyer flasks containing MBH medium plus a selected model NA at
200 mg·L-1. The model NAs tested as growth substrates for the isolates included
cyclohexaneacetic acid (CHAA), cyclohexanecarboxylic acid (CHCA), and
cyclohexanepentanoic acid (CHPA). The NA stock solutions were prepared by dissolving
240 mg of the model NA in 40 mL of alkaline water to a final concentration of (6.0 g · L-
1). The stock solutions were filtered throught a 0.2 µm membrane filter (Millipore) and
transferred to a sterile bottle. Sterile (no inoculum) and substrate free (no substrate
added) controls were also established and monitored. All flasks were covered with a
foam stopper to allow for sterile but aerobic conditions. The flasks were incubated on a
rotatory shaker in the dark at 100 rpm and 30C. Optical density (OD) at 600 nm was
measured every day on a UV 1800 spectrophotometer Shimadzu. Subsamples from the
culture (40 mL) were withdrawn as OD600 values increased. The samples were acidified
with hydrochloric acid (HCl) to pH = 2 to stop the microbial growth, and then subjected
to organic extraction.
Prior to organic extraction of the acidified cultures, 1 mL of octanoic acid was
added as an extraction standard (100 mg · L-1).
The acidified subsamples were then extracted with three volumes of
dichloromethane (DCM) (15 mL each). The combined organic fractions were dried over
anhydrous sodium sulfate and concentrated by rotary evaporation and under a stream of
nitrogen to a volume of 100 µL. The samples were then silylated with 100 µL of N,O-
108
Bis(trimethylsilsyl)trifluoroacetamide (BSTFA) (Thermo Scientific, Waltham, MA) for
20 min at 60 °C.
Naphthenic acids and potential metabolites were analyzed using an Agilent 7890A
gas chromatograph equipped with an HP-5 MS column (30 m 0.25 mm 0.25 µm film;
Agilent Technologies) and an Agilent 5975C mass selective detector. The oven was held
at 45 °C for 5 min, increased at a rate of 4 °C per min to 270 °C, and then held at this
temperature for 5 min. The injector was operated in split mode (50 : 1) and was held at
270 °C. Naphthenic acid degradation was calculated by comparing the peak areas with
the extraction standard, and metabolite identifications were either positively confirmed
by comparing with the mass spectral profiles of pure compounds if available or
tentatively identified by the mass spectral profiles.
5.3 Results
5.3.1 Potential for sulfide oxidation at the surface of tailings pond
Tailings samples from 0 to 9 mbs were used to determine whether sulfide oxidation
in tailings ponds is due to chemical and/or microbial processes. Figure 5-1 shows typical
results of the sulfide oxidation tests, where sulfide was oxidized almost completely
within 80 to 100 min following the addition of air (~20% as O2). This was observed both
in the samples containing non-autoclaved (“live”) tailings and in controls containing
medium only or autoclaved tailings.
109
Figure 5-1 Sulfide loss over time in medium with 3 mM HS- and live or autoclaved
tailings. Controls with medium only were also included. Sulfide concentrations were
measured following amendment with air. (A) Surface water from pond 6 2008, (B)
tailings from pond 6 2008 from depths: 4.5 – 6 mbs. Error bars represent the
standard error of two replicates.
0
0.5
1
1.5
2
2.5
3
3.5
0 20 40 60 80 100 120
HS
-(m
M)
Time (min)
Medium + O2
Medium +autoclaved sample + O2
Medium + sample + O2
A
B
0
0.5
1
1.5
2
2.5
3
3.5
0 20 40 60 80 100
HS
-(m
M)
Time (min)
Medium + O2
Medium + sample (4.5 mbs) + O2
Medium + sample (6 mbs) + O2
110
5.3.2 Microbial community composition of surface waters
Organisms affiliating with the phylum Proteobacteria dominated the water samples
examined in this study [Figure 5-2 (A)], when all samples were pooled and averaged.
Other phyla such as Chloroflexi, Bacteroidetes, Actinobacteria, Cyanobacteria,
Planctomycetes, and Acidobacteria were also present but as lower percentages of
pyrosequencing OTUs. At the genus level, differences in abundance and types of
microorganism were observed among the pond water samples [Figure 5-2 (B)]. The pond
6 2008 sample was abundant in Pedomicrobium sp. whereas surface water samples for
that same pond sampled two years later was dominated by Porphyrobacter sp. In the
water sample obtained from pond 5, Porphyrobacter was also dominant together with
Flavobacterium sp. Other genera like Brevundimonas, were also present in pond 5 2009.
For the surface water, other phyla refers to approximately 16 phyla present with less than
3 % abundance whereas other genera refers to approximately 150 genera present in these
samples at also low abundance (< 3%) [Figure 5-2].
Pond 5 2009 and pond 6 2011 seem to be microbiologically more related than the
two pond 6 samples. Figure 5-3 shows these two samples clustering together. However,
this could be due to the lack of diversity found in samples from pond 6 2008,
corroborated by the low Shannon index when compared with the other two samples
[Appendix Nine:Table 0-8].
111
Figure 5-2 Most abundant pyrosequencing OTUs in tailings surface water from
pond 6 2008, pond 5 2009, and pond 6 2011. (A) Average % of the pyrosequencing
OTUs at the phylum level, (B) % of pyrosequencing OTUs at the genus level for the
years 2008, 2009, 2010. The ‘other genera’ label indicates the genera that were
present at less than 3 % abundance.
A
B
0 20 40 60 80 100
surface
water
Average % of pyrosequencing OTUsProteobacteria
Chloroflexi
Bacteroidetes
Actinobacteria
Cyanobacteria
Planctomycetes
other phyla
0 20 40 60 80 100
P62008
P52009
P62011
% of pyrosequencing OTUs
Porphyrobacter
Flavobacterium
Pedomicrobium
Brevundimonas
other genera
112
Figure 5-3 Relational tree for TPW samples (P62008, P52009, P62011). Bray-Curtis
dissimilarity was used to calculate the distance.
113
5.3.3 Biodegradation experiments with NA isolates
Three bacterial isolates capable of growing on selected NAs were obtained: an
Acidovorax sp., a Xanthobacter sp., and Pseudomonas putida strain ER28 [Table 5-1].
The blasted DNA sequences used for the isolate genus identification are listed in
Appendix One:.
In the time-course biodegradation experiments, all the strains were found to
biodegrade the model NAs effectively in less than 3 d[Figure 5-4]. All the strains showed
a direct relationship between growth increase and degradation of the compound with
maximum degradation during the exponential growth phase. Acidovorax sp. produced
more biomass than P. putida. (e.g. higher OD600 was observed) but the latter had a faster
growth rate. On the other hand, Xanthobacter sp. had variations in its growth
measurements due to the formation of clumps or biofilm that adhered to the walls of the
flask. The degradation of CHPA took slightly longer than CHAA and CHCA. In all
cultures, no substrate was detected in the medium after 6 d incubation [Figure 5-4]. No
growth was observed in substrate-free controls, and no substrate loss was detected in
sterile controls (not shown).
114
Table 5-1 Surface tailings pond water isolates obtained and grown on model
naphthenic acids
strain ID based on 16 S PCR BLAST Model NAs
ER10 Acidovorax sp. Cyclohexaneacetic acid (CHAA)
ER19 Xanthobacter sp. Cyclohexanecarboxylic acid (CHCA)
ER28 Pseudomonas putida Cyclohexanepentanoic acid (CHPA)
115
Figure 5-4 Time course biodegradation experiment of (A) Acidovorax sp. grown on
CHAA; (B) Pseudomonas putida grown on CHPA; and (C) Xanthobacter sp. grown
on CHCA. NA values are the GC-MS peak areas for the derivatized model NA
relative to the peak area of the derivatized extraction standard octanoic acid. Error
bars represent the standard error of three replicates.
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.0
0.2
0.4
0.6
0.8
1.0
0 2 4 6 8
OD
(60
0 n
m)
CH
CA
rel
ativ
e to
std
Time (days)
CHCA
Xanthobacter sp.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0
10
20
30
40
50
0 2 4 6 8
OD
(60
0 n
m)
CH
AA
rel
ativ
e to
std
Time (days)
CHAA
Acidovorax sp.
0
0.02
0.04
0.06
0.08
0.1
0.12
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8
OD
(60
0 n
m)
CH
PA r
elat
ive
to s
td
Time (days)
CHPA
P. putida
A
B
C
116
5.3.4 Naphthenic acid metabolite analysis
GC-MS analysis showed that after the third day of incubation several different
metabolites were detected. Table 5-2 shows the structure of putative metabolites from
CHPA degradation by P. putida and CHCA degradation by Xanthobacter sp.
Xanthobacter sp. metabolized CHCA to cyclohexene carboxylate; however no
other metabolites were observed. For CHPA, different metabolites were detected
suggesting a -oxidation pathway for degradation [Figure 5-5].
Figure 5-6 shows the mass spectra and chemical structures of the putative
metabolites identified during the degradation of CHAA. The Acidovorax sp. isolated was
the only one of the three able to biodegrade CHAA [Figure 5-6]. Some metabolites were
the same as those detected in the other cultures (e.g. cyclohexanecarboxylate and
cyclohexenecarboxylate) but other new metabolites were detected [Figure 5-6],
suggesting other mechanisms of biodegradation [Figure 5-7].
117
Table 5-2 Summary of metabolites detected from the degradation of CHCA by
Xanthobacter sp. and CHPA by Pseudomonas putida growing on these substrates as
their only carbon source. Compounds indicated with an asterisk were only
tentatively identified due to lack of authentic standards.
Metabolite Chemical structure Xanthobacter sp.
ER19
Pseudomonas
putida
ER28
Cyclochexanecarboxylic
acid (CHCA)
Cyclohexenecarboxylic
acid
*Cyclohexanepropionic
acid
Cyclohexene propionic
acid
Cyclohexene 1,4 –
dicarboxylic acid
*3- carboxy-propionic
acid
118
Figure 5-5 Proposed biodegradation pathway of CHPA via -oxidation by P. putida
strain ER28. Compounds indicated with an asterisk were only positively identified;
others were only tentatively identified due to lack of authentic standards.
C5
C3
C1
-oxidation
-oxidation
CO2 + H2O???
-oxidation
*
*
*
*
*
119
Figure 5-6 Mass spectra of metabolites detected (as silylated derivatives) after 3 d
incubation of Acidovorax sp. strain ER10 with CHAA (100 mg · L-1
) as the sole
source of carbon. The bacterium was grown on MBH, incubated in the dark at 30
C and at 100 rpm. The metabolites were not detected in the sterile controls.
60 80 100 120 140 160 180 200 220 240 260 280
73 185
55117
14599 200
60 80 100 120 140 160 180 200 220 240 260 280 300
183
79108
13953 198
157
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340m/z-->
147
73
273117 183 204
288
Rel
ativ
e A
bund
ance
M+ = 200
M+-15 = 185
M+ = 198
M+-15 = 183
M+ = 288
M+-15 = 273
cyclohexanecarboxylate
cyclohexenecarboxylate
2-hydroxy-
cyclohexane
carboxylate
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
73
171
147
287259204 231117
302
or
m/z
60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360
122 197
75
168
212
153
94
m/z
M+ = 212
M+-15 = 197
Cyclohexylidene
acetic acid?
M+ = 302
M+-15 = 287
m/z
m/z
120
Figure 5-7 Proposed biodegradation pathway of model NA cyclohexaneacetic acid
by Acidovorax sp. strain ER10. Compounds indicated with an asterisk were only
tentatively identified due to lack of authentic standards. Pathways shown have
previously been reported for Arthrobacter 153
and Alcaligenes sp .78
.
Cyclohexane
acetic acid
Acidovorax sp. ER10
C6 acid
(adipic)
C7 acid
(pimelic)
AlcaligenesArthrobacter
*
*
*
*
*
*
??
CH3COO-
CO2
-oxidation-oxidation
lyase
121
5.4 Discussion
Tailings pond surface water presents a different microbial community than the rest
of the pond mainly due to differences in the water chemistry, low proportions of solids
(i.e. less available reactive surface area), and the availabiity of oxygen as an electron
acceptor. The high concentration of sulfate measured [section 4.3.1.2, Figure 4-8 (A)],
and the aerobic nature of these waters allowed us to postulate that sulfate is the result of
SOB activity. However, our results indicate that sulfide is mainly oxidized chemically
when tailings are exposed to air. In samples from all depths tested, however, the sulfide
concentration did decrease more rapidly and to a greater extent in the tests containing the
“live” tailings than in the controls [Figure 5-1]. The 454 pyrosequencing results did not
reveal a rich SOB population with the exception of samples from pond 6 2008 where 5
% of the pyrosequencing OTUs comprised the budding-like bacteria Pedomicrobium
[Figure 5-2]. Members of this genus have previously been reported to be involved in the
oxidation of volatile sulfur-containing compounds, including H2S 154
. Considering that
pond 6 in 2008 was completely active and concentrations of sulfate were the highest in
comparison with the rest of the sampling times, [2010, 2011, section 4.3.1.2, Figure 4-8
(A)], we can infer these bacteria may have been involved in the oxidation of sulfide to
sulfate during this time. In addition, among the cultivation and isolation of NA degraders
from TPW, some isolates of Xanthobacter have previously been reported to oxidize
sulfide to sulfate via thiosulfate 155
. In TPW, species affiliated with this genus were
found, ranging from 0.05 to 2.2 % of pyrosequencing OTUs. This suggests that if some
H2S escapes to the surface of the pond, some SOB activity could take place in the water
layer. However, chemical sulfide oxidation is probably dominant.
122
Based on the identities obtained by pyrosequencing, we can infer that the majority
of the microorganisms present in TPW are more likely to be involved in the degradation
of NA and hydrocarbon-like compounds. In fact, in addition to Xanthobacter sp., a
Pseudomonas sp. (isolated herein and also studied for NA biodegradation), appeared in
the sequencing results from TPW of ponds 5 and 6 (data not shown due to percentage of
abundance being less than 3 % of pyrosequencing OTUs). Other organisms like
Porphyrobacter sp., that dominated TPW from ponds 5 and 6 in the years 2009 and 2011
respectively, have previously been detected in tropical land farm soils contaminated with
oil waste 156
. Organisms in this genus are mainly found in association with algae and
cyanobacteria accomplishing anoxygenic photosynthesis 157
. These species could well be
co-metabolizing NAs with algae in TPW, as previous studies have shown algae in TPW
with promising NA biodegradation capabilities 158,159
. The rest of the genera found in
pond 5 and 6 during the years 2009 and 2011, are also related to the biodegradation of
hydrocarbon like compounds including Brevundimonas sp. 160-162
, Xanthobacter sp. 163
,
and Pseudomonas sp. 133,164,165
.
It should be pointed out that TPW from pond 6 2008 did not show as much
diversity as the other two surface waters sampled, probably due to DNA extraction
biases. The DNA extraction protocol (FastDNA
kit) recomends that for liquid samples a
volume of 200 µL with suspended cells of 109 bacteria should be used. However, for our
TPW samples, the number of cells was not known (not measured) as they were
environmental samples. It is possible that the number of organisms was lower than
123
recommended therefore more volume of water was initially needed to achieve the
manufacture’s recommendations.
Some previous work has demonstrated metabolic pathways by which NA may be
degraded. For example, NA with odd-numbered fatty acid side chains (e.g. C1, C2, C3)
have been shown to be biodegraded by -oxidation 150,151
. In particular, Pseudomonas
putida has been previously reported as a NA-biodegrading organism 64,76,166
. The -
oxidation pathway seems to be the preferred route by which this bacterium degrades NAs
82. This oxidation route involves the formation of new carboxylic acids with two carbons
fewer than the parent compound 82
.. Based on the metabolites detected in our
experiments, the degradation of CHCA, by Xanthobacter sp., and CHPA by P. putida,
both presumably occurred via by -oxidation [Figure 5-5], confirming previous literature
results.
Xanthobacter sp., although not previously reported as NA degraders, in general are
characterized by their ubiquitous distribution in the environment, and metabolic
versatility 167
. Some species like Xanthobacter autotrophicus exhibit
chemolithoautotrophy, methylotrophy, short-chain hydrocarbon metabolism, and
chlorinated hydrocarbon metabolism 168
. Others like X. tagetidis can grow as a
chemolithotrophic autotroph on thiosulfate or as a heterotroph on thiophene – 2 –
carboxylic acid, acetic acid and -ketoglutaric acid, and as a mixotroph on a combination
of thiosulfate and thiophene – 2 – carboxylic acid and/or acetic acid . Our observation
that Xanthobacter is able to biodegrade model NA extends the known metabolic diversity
of this genus.
124
In contrast to odd-numbered compounds, biodegradation of even alkyl chain NAs,
such as cyclohexaneacetic acid (CHAA), does not occur by -oxidation due to a blockage
by the relative positions of carboxy group and cyclohexane ring 78
. The degradation of
this compound needs either a lyase or - oxidation process followed by a -oxidation 78
.
Two different pathways have been proposed, one in a marine bacterium Alcaligenes sp.
78, and the other in Arthrobacter sp. [Figure 5-7]. Neither of these organisms was
isolated from TPW, but rather an Acidovorax sp. capable of degrading CHAA was
isolated. In the CHAA – degrading experiments with Acidovorax sp., several metabolites
were positively and tentatively identified. Based on the compounds detected, however, it
could not clearly be deduced which pathway was being used by the Acidovorax sp. as
putative metabolites from each pathway were detected [Figure 5-7]. Future work using
labelled NA substrates or more detailed time course experiments may help further
identify which pathway, or whether a novel pathway is being used by the Acidovorax sp.
to degrade CHAA and related compounds. Nevertheless it is clear that the isolates
obtained from TPW were able to transform the model NAs into other compounds,
showing evidence of biodegradation. Although CO2 production and/or molar mass
balance were not measured, these isolates may serve as model organisms that can be used
to further study the biodegradation of more complex NA. Although not directly a part of
this thesis work, the isolates have now been sent for genome sequencing. From this, key
genes and regulatory elements involved in NA biodegradation in general can be
identified.
125
Chapter Six: Targeting specific microbial functions in oil sands tailings ponds by
quantitative PCR.
6.1 Introduction
As demonstrated in previous chapters, the main microbial activities observed in
tailings ponds involve the sulfur and the one-carbon (C1) cycles. The addition of calcium
sulfate as a tailings densification agent can promote sulfate reduction, subsequently
producing hydrogen sulfide 3. When sulfate concentrations are relatively low (~ 2 mM),
methanogens start to dominate, making the production of methane a concern in tailings
ponds 44
. Desulfocapsa sp./Thiobacillus sp. may be the key players in sulfur metabolism
while Methanosaeta sp./Methanolinea sp. are the leading methanogens (Chapter Four). It
was also seen that at some depths, there are “pockets” of sulfate that are not being
reduced by SRB, probably due to the lack of biodegradable electron donors or possibly
due to SOB metabolism potentially oxidizing sulfide to sulfate. To further characterize
these microbial processes, additional measurements were carried out.
An approach that can be used to identify key microbes taking the lead in these
processes, is by targeting specific genes that are known to participate in the sulfur
oxidation/ reduction metabolism (sox and dsr genes) and methane production pathways
(mcrA gene). Quantitative PCR (qPCR) can be very helpful to numerically estimate the
distribution of microbial communities participating in these mechanisms 169
. In this
method, fluorescenct dyes like SYBR green (Applied Biosystems) bind to the PCR
products during thermal cycling. Increased fluorescence in every cycle is measured in the
126
extension step for each cycle of the PCR reaction. This is converted to the gene copy
number of a given gene by comparing with a set of standards with known copy numbers.
For example, by targeting and quantifying the dsrB gene, we can estimate the
distribution of SRB present in the pond more accurately than with the 16S rRNA gene
170,171. Just to cite some examples, amplification of SRB genes has been targeted in
produced waters from an oil field 169
and in a bioreactor simulating souring in a low-
temperature oil reservoir 172
. Likewise, methanogenic Archaea 171,173,174
, and sulfite
oxidoreductases 175
have been monitored by qPCR by targeting the mcrA and sox genes,
respectively. This chapter describes the results of targeting specific functional genes for
key processes in oil sands tailings ponds (methanogenesis and sulfate reduction and
sulfide oxidation) and compares them with other depth-dependent physiological
measurements.
6.2 Methods
6.2.1 DNA extraction and selection of functional genes
For this study, genomic DNA extracted from all depths from pond 6 (2008, 2010
and 2011) was used as the DNA template for qPCR studies. Pond 6 is somewhat active
therefore it is a good model to study and understand the distribution of particular genes in
tailings ponds. For more details about pond 6, and DNA extraction protocols (with skim
milk powder), please refer to sections 4.2.1 and 3.4.1. Table 6-1 lists the genes targeted
in this study and their corresponding enzymes and metabolic activities.
127
Table 6-1 List of genes used for qPCR and their corresponding enzyme and
metabolic activity.
gene enzyme Metabolic pathway
dsrB dissimilatory sulfite
reductase
Catalyzes the six-electron reduction of
(bi)sulfite to sulfide, in dissimilatory
sulfate respiration 176
mcrA subunit of methyl
coenzyme-M reductase
Terminal enzyme complex in the
methane generation pathway. Catalyses
the reduction of a methyl group bound
to coenzyme-M with the concomitant
release of methane 177
sox Sulfite oxidases*
Group of enzymes that catalyses the
oxidation of sulfite or thiosulfate to
sulfate 62,178
* Biologically-produced sulfate in tailings ponds is produced by via sulfite by sulfite
oxidases [Appendix Five:].
128
6.2.2 Primer design
The real time quantitative PCR primers for dsrB, mcrA, and sox genes were
designed from sequences obtained from the metagenome of DNA extracted from tailings
pond 6, sampled in 2008 and 2010 (unpublished data). For the metagenome, DNA was
extracted using Fast DNA Spin Kit for Soil (MP Biomedicals) giving a total yield of 3 µg
of DNA.
A list of the functional genes obtained for this metagenome was acquired through
the Integrated Microbial Genome (img/mer) web page linked to the JGI website
[https://img.jgi.doe.gov/cgi-bin/mer/main.cgi] through the KEGG (Kyoto Encyclopedia
of Genes and Genomes) database. Twelve primer sequences were designed and
optimized for qPCR [Table 6-2].
129
Table 6-2 Designed primer sequences to test for optional qPCR amplification of
dsrB, sox, and mcrA genes based on the pond 6 (2008/2010) metagenome.
Sequence No. Primer name 5’ primer sequence 3’
1 DSR1F 5’- CAGGGYTGGRTMCACTGCCAYA-3’
2 DSR1R 5’- ACVGCRCCRCACATRTTCA – 3’
3 DSR2F 5’- CAGGGYTGGRTMCACTGCCA-3’
4 DSR2R 5’- GCRCCRCACATRTTCAGSCA-3’
5 SOX1F 5’-CGGTTACCCGCTGCGWCTC-3’
6 SOX1R 5’- TGRTGTGCGYATCTGTCT-3’
7 SOX2F 5’-GTTACCCGCTGCGWCTCRTSGT-3’
8 SOX2R 5’- GCGYATCTGTCTTCTGGGYCG-3’
9 MCR1F 5’-ATGCTNTWCGACCARA-3’
10 MCR1R 5’-ATRTTGTCNGTGTAKGCMGCGGT-3’
11 MCR2F 5’-GCTNTWCGACCARATCTGG-3’
12 MCR2R 5’-GTGTAKGCMGCGGTWGCRTA-3’
130
6.2.3 Primer optimization, cloning, and qPCR assay
6.2.3.1 Primer optimization
To optimize dsrB primers, genomic DNA from Desulfovibrio vulgaris
Hildenborough was used. For the mcrA and sox genes, toluene enrichments under
methanogenic conditions and a nitrate-reducing enrichment from souring bioreactors
were used, respectively. Good quality primers were chosen based on the size and purity
of the expected PCR product visualized on a 1.5 % agarose gel.
The primer optimization tested for different annealing temperatures (Ta) that
yielded the single PCR product (e.g. most pure, correct size). The PCR mixture
comprised 12.5 μL of 2xPCR Master Mix (Fermentas), 10.5 μL of nuclease-free water
(Fermentas), 1 μL of genomic DNA (2 ng) and 0.5 μL of the specific primer (20 pmol
μL-1) for a 25 μL PCR reaction. The PCR program used is described in section 3.4.2.
6.2.3.2 TOPO TA cloning
The resulting PCR product from each amplification was purified using the QIA
PCR purification kit (Qiagen), quantified using a Qubit Fluorometer (Invitrogen), and
ligated into a TOPO PCR 2.1 plasmid vector at a 1:1 plasmid-PCR ratio. Cloning of the
ligated product was achieved according to the manufacturer’s protocol (Invitrogen).
From each kanamycin (kan) LB plate spread with the product of interest, at least 6 white
to light blue colonies were selected. The positive colonies were transferred to kan-LB
broth for 24 h incubation followed by plasmid purification with Qiaprep Spin Miniprep
kit (Qiagen). The plasmid was then PCR amplified with same primer set and PCR
131
program as previously described. The concentration of each selected plasmid was
determined by fluorimetry and the gene copy number was calculated 179
. Quantitative
PCR standard solutions were made with quantified plasmid. Stock standard solutions
were serially diluted from 102 copies · µL
-1 to 10
8 copies · µL
-1 in a final volume of 200
µL. Each dilution was then PCR amplified to check for purity of the product.
6.2.3.3 Quantitative PCR assay
“Real-time” PCR was performed in a Rotor-Gene Q (Qiagen) quantitative
thermocycler and the data were analyzed using Rotor Gene Q software (Qiagen). The
reactions were performed in 0.2 mL PCR tubes for real-time PCR (Qiagen).The PCR
samples had 12.5 µL total volume and contained 6.25 µL Reaction Mix, 0.3 µL each of
forward and reverse primers (500 nM); 4.65 µL of qPCR grade water and 1.0 µL of
genomic DNA. The real-time PCR reaction was subjected to the programs shown in
Table 6-3 depending on the particular gene.
Software-derived standard curves were generated for dsrB (R2=0.992,
efficiency=0.9459, and slope=-3.459); mcrA (R2= 0.993, efficiency= 1.105, and slope= -
3.093 ); and sox (R2= 0.980, efficiency=1.29, and slope= -2.776). Melt curve analysis
was performed on all samples and no significant primer dimers were detected.
To rule out false positives, a no template control (NTC) was used as negative
control. Skim milk powder DNA was also PCR quantified and subtracted from all the
samples. The percentage of the functional genes normalized to the total 16S rRNA gene
was calculated. All samples, standards, and NTC were done in triplicate.
132
Table 6-3 real time PCR program for each particular gene
gene PCR program
dsrB 95 C for 3 min; 30 cycles of: 95 C for 30 s; 55 C for 45 s: data
acquisition
mcrA 95 C for 5 min; touchdown decreasing 1 C every cycle for 40 cycles
[95 C for 30 50 C for 45 s; 57 C for 60 s]: data acquisition
Sox 95 C for 10 min; 40 cycles of: 95 C for 30 s; 57 C for 45 s: data
acquisition
16S rRNA 95 C for 10 min; 40 cycles of: 95 C for 10 s; 60 C for 30 s: data
acquisition
133
6.3 Results
6.3.1 Functional gene primers selected and qPCR
Table 6-4 lists the set of primers selected and their corresponding optimized
annealing temperature (Ta) and amplicon size in base pairs. The copy number obtained
for each sample was converted into gene copies per gram of wet tailings.
The genes targeted (dsrB, mcrA, sox) were detected in all the tailings depths
evaluated, although dsrB and mcrA were more abundant [Figure 6-1]. Comparing the 3
years of sampling, pond 6 2008 is more dominated by communities that contained the
dsrB genes whereas in the pond 6 2010 samples the mcrA gene is more dominant
throughout the pond [Figure 6-1, Table 6-5]. The proportions of dsrB and mcrA for pond
6 2011 are relatively close [Table 6-5]. Interestingly, sox genes were relatively low in
abundance and not present in the surface samples. Pond 6 2008 had a very homogeneous
distribution of dsrB and mcrA in the pond [Figure 6-1(A)] with gene copy numbers per g
of tailings averaging 4.7 x 107 and 2.8 x 10
7, respectively. Similarly for pond 6 2010, the
average gene copy numbers per g of tailings were 3.8 x 107 for dsrB and 8.1 x 10
7 for
mcrA. Pond 6 2011 appeared more stratified, with the greatest gene copy numbers at the
top and bottom of the of the MFT layers [Figure 6-1(B)]. For these samples, the average
gene copy number per g of tailings were 9.6 x 107 and 7.1 x 10
7 for dsrB and mcrA
genes, respectively.
134
Table 6-4 Set of primers selected for functional gene study in tailings and their
optimal annealing temperature (Ta), amplicon size, and copy number obtained
from each reference organism.
Set of primers Ta (C) Amplicon size (bp) Copy number
dsr1f/dsr2r 55 145 5.4 x 109
sox2f/sox2r 57 94 1.1 x 1010
mcr1f/mcr1r 50 90 1.0 x 1010
16S rDNA
341f/534r
60 193 7.2 x 108
135
Figure 6-1 Gene copy number of specific genes (dsrB, mcrA, sox) per gram of
tailings, quantified in tailings samples from pond 6. (A) Sampled in 2008, (B)
Sampled in 2010, and (C) Sampled in 2011. (▲) sox, (●) mcrA, and (□) dsrB.
A B
C
0
5
10
15
20
25
0.00E+00 1.00E+08 2.00E+08
Dep
th (
mb
s)
gene copy # · g tailings-1
P62008
0
5
10
15
20
25
0.00E+00 1.00E+08 2.00E+08
Dep
th (
mb
s)
gene copy # · g tailings-1
P62010
0
5
10
15
20
25
0.00E+00 1.00E+08 2.00E+08
Dep
th (
mb
s)
gene copy # · g tailings-1
P62011
136
The percentage of each functional gene contained in relation tothe total amount of
16S rRNA genes quantified, shows that out of the total 16S rRNA gene, pond 6 2008 and
pond 6 2011 have higher numbers of dsrB genes with respect to mcrA [Table 6-5]. For
pond 6 2008, the abundance of dsr genes is almost double that of of mcrA but for pond 6
2011, less of a difference is observed [Table 6-5]. On the other hand, in pond 6 2010 the
proportion of dsrB genes with respect to mcrA is the opposite wherein mcrA gene copy
numbers are double those of dsrB genes. Sox genes are the least abundant for all the
samples studied [Table 6-5], with gene copy numbers averaging 106 and 10
7 for all the
tailings samples, one to two orders of magnitude lower than for the dsrB and mcrA genes.
137
Table 6-5 Average percent of functional genes normalized to the total 16S rRNA
genes. These values are obtained by dividing the copy number of each particular
gene by the copy number of the 16S rRNA for each depth, and then averaging the
values of all depths for each pond.
Pond sample dsrB(%) mcrA(%) Sox(%)
P62008 51.2 28.5 5.9
P62010 7.9 16.1 1.6
P62011 70.0 56.8 8.4
138
6.3.2 Correlation of functional genes with microbial activity and chemistry
composition as a function of depth in the tailings samples.
The pattern of dsrB gene numbers measured in the pond 6 2008 samples correlates
well with the SRR and abundance of Desulfocapsa as a function of depth [Figure 6-2(A,
B, C)]. For example, all three measurements show evidence for elevated sulfate reduction
from 12 to 15 mbs. Microorganisms containing the sulfite oxidases (Sox) were also
highly detected at these same depths but appeared to correlate most closely with
Thiobacillus sp. and the SRR profile [Figure 6-2(B, D, E)].
Rates of methanogenesis showed a fluctuating distribution throughout the pond for
the 2008 samples [Figure 6-2 (G)]. This pattern positively correlated with the mcrA gene
quantification as a function of depth [Figure 6-2 (F, G)]. However, the mcrA gene
quantification profile did not closely parallel any particular taxon of methanogens [Figure
6-2 (H, I, J)]. Nevertheless, the mcrA gene depth-dependent profile is consistent with the
abundance of different taxa at different levels of the pond; Methanosaeta and
Methanolinea likely contribute to CH4 production at the upper depths [Figure 6-2 (H)],
Methanospirillum and Methanosarcina in the middle [Figure 6-2 (I)],
Methanomethylovorans and Methanobacterium contribute to CH4 production in the
deeper zones [Figure 6-2(J)].
139
Figure 6-2 Correlation between qPCR of the functional genes (dsrB, mcrA, sox), in
pond 6 2008 with the microbial activity and key microbial genera detected by 16S
rRNA gene sequencing. (A) dsrB gene, (B) SRR, (C) % of abundance of
Desulfocapsa sp., (D) sox gene, (E) % of abundance of Thiobacillus sp., (F) mcrA
gene, (G) methane production rate, and (H,I,J) % abundance of methanogen taxa
present in pond 6 2008 samples. Error bars obtained from three replicates are on
the order of 102 for the PCR data analyses (not visible).
0
5
10
15
20
0.00E+00 2.00E+07gene copy#/g tailings
sox
0
5
10
15
20
0 2 4 6 8
Desulfocapsa sp.
% of pyrosequencing
OTUs
0
5
10
15
20
0.00E+00 5.00E+07 1.00E+08
gene copy # /g tailings
dsrB
0
5
10
15
20
0 20 40 60
nmol cm-3 d -1
SRR
0
5
10
15
20
0 5 10 15% of pyrosequencing
OTUSs
Thiobacillus sp.
0
5
10
15
20
0.E+00 5.E+07 1.E+08
gene copy#/g tailings
mcrA
0
5
10
15
20
0 50 100nmol cm-3 d-1
Methane production
A B C
D E
0
5
10
15
20
0 5 10
% of pyrosequening OTUs
Methanomethylovorans
Methanobacterium
0
5
10
15
20
0.00 0.05 0.10
% of pyrosequencing OTUs
MethanospirillumMethanosarcina
0
5
10
15
20
0 50 100
% of pyrosequencing OTUs
MethanosaetaMethanolinea
F G
H I J
Dep
th (m
bs)
140
Correlation analysis for the pond 6 2010 and 2011 samples were similar to that
obtained for pond 6 2008. For example, the abundance of Desulfocapsa sp. mirrors the
SRR and the copy number for the dsrB gene [Figure 6-3 (A, B, C,) and Figure 6-4 (A, B,
C)], while the % abundance of Thiobacillus sp. matches with that of the sox gene and
SRR [Figure 6-3 (D, E) and Figure 6-4 (D, E)]. For pond 6 2010, sulfate reduction and
sulfite oxidation potential is near the more shallow depths of the pond [Figure 6-3 (B,
D)]. However in these samples, the sox gene profile does not correlate as closely with
Thiobacillus sp. abundance [Figure 6-3 (D, E)] as was observed in the pond 6 2008
profiles [Figure 6-2 (D, E)], although % abundance of Thiobacillus sp. is also
comparatively low. Further, in the 2010 samples, the mcrA gene copy numbers also did
not correlate well with the rates of methanogenesis or the % abundances of the dominant
methanogens.
For pond 6 2011, sulfate reduction and sulfite oxidation processes are more
towards the top and bottom of the pond [Figure 6-4 (A, B, C, D, E). For the pond 6 2011
samples, the sox gene copy numbers closely paralleled the % abundance of Thiobacillus,
especially at the deeper depths [Figure 6-4 (D, E)] (compared to the 2010 samples). The
mcrA gene copy numbers closely aligned with % abundance of the dominant methanogen
(Methanolinea sp.) and the methanogenesis rates, especially at the shallower depths
[Figure 6-4 (F, G, H)].
Overall, the dsrB gene profiles aligned well with SRR and SRB abundance in all
years sampled. The sox and mcrA genes closely mirrored microbial taxa and/or activity in
teh 2008 and 2011 samples, but did not correlate as well with these other measurements
for the 2010 samples.
141
Figure 6-3 Correlation between qPCR of the functional genes (dsrB, mcrA, sox), in
pond 6 2010 with the microbial activity, and key microbial genera detected by 16S
rRNA gene sequencing. (A) dsrB gene, (B) SRR, (C) % abundance of Desulfocapsa
sp., (D) sox gene, (E) % abundance of Thiobacillus sp., (F) mcrA gene, (G) methane
production rate, and (H) % abundance of methanogen taxa present in pond 6 2010
samples. Error bars obtained from three replicates are on the order of 102 for the
qPCR analyses (not visible).
0
5
10
15
20
25
0 10 20
% of pyrosequencing OTUs
Methanolinea Methanosarcina
0
5
10
15
20
25
0.00E+00 5.00E+07 1.00E+08
dsr copy # /g tailings
dsrB
0
5
10
15
20
25
0.0 1.0 2.0
(nmol cm-3 d -1)
SRR
0
5
10
15
20
25
0.00E+00 1.00E+08 2.00E+08
mcr copy # /g tailings
mcrA
0
5
10
15
20
25
0 2 4 6
% of pyrosequencing OTUs
Desulfocapsa sp.
0
5
10
15
20
25
0.0E+00 1.0E+07 2.0E+07
sox copy # /g tailings
sox
0
5
10
15
20
25
0.00 0.20 0.40
nmol cm-3 d-1
Methanogenesis rate
A B C
D E
F G
0
5
10
15
20
25
0 0.5 1
% of pyrosequencing OTUs
Thiobacillus sp.
HDep
th (
mb
s)
142
Figure 6-4 Correlation between qPCR results of the functional genes (dsrB, mcrA,
sox), in pond 6 2011 with the microbial activity, and microbial genera detected by
16S rRNA gene sequencing. (A) dsrB gene, (B) SRR, (C) % of abundance of
Desulfocapsa sp., (D) sox gene, (E) % abundance of Thiobacillus sp., (F) mcrA gene,
(G) methane production rate, and (H) % of abundance of Methanolinea sp. Error
bars obtained from three replicates are on the order of 102 for the qPCR data
analyses (not visible).
0
5
10
15
20
0 1 2 3
% of pyrosequencing OTUs
Thiobacillus sp.
B
0
5
10
15
20
0.00E+00 1.00E+08 2.00E+08
dsrB copy #/ g tailings
dsrB
0
5
10
15
20
0.00E+00 1.00E+07 2.00E+07 3.00E+07
sox
0
5
10
15
20
0.00E+00 1.00E+08 2.00E+08
mcrA copy #/g tailinsg
mcrA
0
5
10
15
20
0 50 100
(nmol . cm-3. d-1)
Methanogenesis rate
0
5
10
15
20
0.00 0.20 0.40(nmol . cm-3 . d-1)
SRR
0
5
10
15
20
0 10 20
% of pyrosequencing OTUs
Methanolinea sp.
A C
D E
F G H
Dep
th (
mb
s)
0
5
10
15
20
0 2 4% of pyrosequencing OTUs
Desulfocapsa sp.
143
6.4 Discussion
Molecular approaches based on 16S rRNA gene sequence analysis have become
the norm to identify microbial community members in different ecosystems. The study of
these sequences allows us to understand the community structure, diversity, and
phylogeny of microbes in their natural environment 180,181
. In particular, quantitative PCR
is a very sensitive method for the quantification of microbes from different samples 182
.
In this study, we quantified the distribution of microbes harboring key functions in an
active tailings pond based on the copy number of genes carrying out sulfate reduction
(dsrB), methane production (mcrA) and sulfite oxidation (sox). Our selected ecosystem
was pond 6 from Suncor Energy Inc., which was monitored over the years 2008, 2010,
and 2011. The metagenome of this pond was recently obtained (unpublished data)
allowing us to design primers to target the genes involved in these main microbial
processes currently ongoing in tailings ponds 16,44
. This increased the accuracy of our
results allowing us to establish correlation studies with the 16S rRNA gene survey and
physiology measurements previously described [Chapter Four].
Initially, the primers were designed to study the actual active microbes in the pond
by targeting RNA. However, failure to extract RNA from tailings prevented us from
determining the actual active gene copy numbers. Hence, the results discussed here are
only based on DNA approaches. However we were able to obtain information regarding
the vertical spatial distribution of potential activities in the pond and compare the profiles
with physiological measurments and key taxa. To our knowledge this is the first time that
quantitive PCR has been used to target functional genes in tailings ponds. Therefore, the
144
results obtained here further broaden the understanding of the active physiology in
tailings ponds.
The percentage of dsrB, mcrA and sox genes relative to the 16S rRNA gene in our
tailings samples, confirms the importance these functions have in tailings ponds, in
particular for the activities of sulfate reduction and methanogenesis [Table 6-5]. Our
results showed an increase of methanogenesis from 2008 to 2010, likely due to a change
in pond management by the operators. In 2008, pond 6 was actively receiving fresh
tailings from the extraction plant (amended with CaSO4) therefore one would expect to
obtain more sulfate reduction (dsrB activity) compared to methanogenesis. However, in
2010 no more fresh tailings were being added to the pond, thus reducing the amount of
electron acceptor available for SRB. Hence, the mcrA percentage was higher with respect
to that of dsrB by 2010 [Table 6-5].These results correspond with what was observed for
the 16S rRNA survey conducted on this pond for the same period (Chapter Four). The
numbers obtained in 2011 were higher than expected; this could be due to the presence of
several gene copy numbers in the microbial population. More experiments need to be
done in order to clarify these results.
The mcrA gene has been used to target methanogenic Archaea in crude oil
hydrocarbon-impacted environments with success, helping in the identification of certain
key taxa 183
and for elucidating certain roles played by this group of microbes 184
. In
addition, the specificity of the mcrA gene has helped to reveal more diversity in the
methanogenic communities than was initially observed with the 16S rRNA in other
studies 185
.
145
Based on the 454 pyrosequencing characterization of the16S rRNA gene, pond 6 is
mainly inhabited by the methanogens Methanosaeta and Methanolinea which are
distributed in a heterogeneous “fluctuating” arrangement throughout all the depths
studied in the pond, but with a tendency to be more abundant in the upper layers of the
pond (Chapter Four). Quantitative PCR confirms the methanogenic characteristic of the
pond but the correlation between these two groups of Archaea and the mcrA gene was not
always congruent. However, for the 2008 samples the mcrA profiles did correlate
positively with the rates of methane production activity as measured in the laboratory
tests. We postulate that this could be due to the presence of a wide variety of
methanogenic taxa that are distributed at discrete depths in the pond. Nine genera of
methanogens were identified to the genus level, but for others the identification only
covered the phylum, class, order or family level [Appendix Two:]
It is known that the mcrA gene is exclusively found in methanogens and in the
anaerobic methane oxidizing Archaea (AMO) 186
. Therefore, another possible
explanation for this lack of similarities between the 16S rRNA gene profile and the mcrA
gene could be that our primers targeted both methanogens and ANME (anaerobic
methanotrophs) in the tailings ponds. In fact, previous microbial community studies in oil
sand samples using 16S rRNA gene sequencing have revealed the presence of ANME –
1a 187
. Our samples did contain Archaea sequences that are phylogenetically similar to
the ANME linages such as Methanosarcinales and Methanomicrobiales 188
although in
relatively low abundance. Similarly, the sulfate reducers thought to be associated with
ANME (within the Desulfosarcina/Desulfococcus cluster of the Desulfobacteraceae 189
),
were also found in our tailings 16S rRNA gene pyrosequencing characterization, in some
146
cases only identified to the family level [Appendix Two:]. No previous research has
reported the presence of ANME in tailings ponds thus, other molecular techniques and
experiments will need to be implemented in order to clarify this.
By contrast, the dsrB gene quantification results correlated well with the SRR
activity and mirrored the profile of the dominant SRB like Desulfocapsa sp. [Figure 6-2,
Figure 6-3, Figure 6-4(A, B, C)]. This finding supports the proposed role that members
affiliated with Desulfocapsa sp. play in the reduction of sulfate in tailings ponds. As was
explained in Chapter Four, members of this genus can serve both as sulfite
disproportionating or sulfate-reducing organisms. We do not out rule the participation of
other groups of SRB such as the sulfur disproportionator Desulfobulbus sp. 190
found in
samples from 2011, or Desulfoglaeba sp. found in 2010 (among others), however,
Desulfocapsa sp. is a common, abundant genus found in all years sampled, so, we can
infer its importance in the sampled tailings pond. Furthermore, the mirroring of
Thiobacillus sp. with SRR activity and sox gene quantification also sheds some light into
the understanding of the sulfur metabolism in tailings ponds. For example, it can be
hypothesized that Thiobacillus sp. and Desulfocapsa sp. may be metabolically
(syntrophically) related. Syntrophic associations based on the interchange of reduced and
oxidized sulfur compounds have been previously described for laboratory experiments of
sulfur oxidizing Thiobacillus thioparus T5 and the sulfate-reducing Desulfovibrio
desulfuricans PA2805 191
. These interactions usually occur under oxygen-limited
conditions where Thiobacillus sp. oxidize sulfide to elemental sulfur and thiosulfate. The
resulting compounds can be used by SRB as electron acceptors while reducing hydrogen
or organic compounds, thereby establishing a close relationship between the two
147
microbes. In addition, sulfur and thiosulfate may also be disproportionated into sulfide
and sulfate, contributing to the continuity of the sulfur cycle. Other interactions like
aggregations between a sulfur oxidizer and a sulfate reducer/sulfur disproportionator
living in the chemocline of a meromictic lake, have also been published 192
. Based on the
discussion above, the interaction between Thiobacillus and Desulfocapsa species in
tailings ponds may be occurring as shown in Figure 6-5. Measurements of Fe (II) in
tailings since 2010 [Appendix Twelve:] suggested that iron reduction is likely also an
important process in tailings, to which Thiobacillus can also contribute[Figure 6-5].
In our tailings samples, Thiobacillus sp. mirrors the vertical distribution in the pond
with that of the sox genes quantified, especially for 2008 and 2011 samples. Members of
bacteria grouped under this genus are very diverse and have been found in different
ecosystems 62
. In our study, we targeted sulfite oxidases which oxidize sulfite to sulfate
[Equation 4].
Equation 4 Enzymatic reaction catalyzed by sulfite oxidases.
The oxidation of sulfur compounds to sulfate has been well studied in Thiobacillus
sp. in particular in the obligately chemolithoautotrophic facultatively anaerobic
bacterium Thiobacillus denitrificans 193
. The sequence of its genome revealed more than
50 genes associated with sulfur-compound oxidation (including sox genes, dsr genes, and
genes associated with the AMP-dependent oxidation of sulfite to sulfate) 193
.
SO32− + H2O → SO4
2− + 2H+ + 2e−
148
Figure 6-5 Proposed mechanism of microbial interaction between Desulfocapsa sp.
and Thiobacillus sp. occuring in oil sands tailings ponds.
SO4 2- HS-S
Sulfite
Desulfocapsa sp.
Thiobacillus sp.
Sulfur disproportionation
Sulfate reduction
Sulfite oxidation
Fe 3+Fe 2+
149
The sulfate yielded by this enzymatic reaction may well be the reason why sulfate
is sometimes abundant at some depths in tailings ponds where all the sulfate should
theoretically be consumed (e.g., in deeper layers). The oxidation of sulfur compounds
coupled to iron reduction has also been well investigated. Providing there is ferric iron
(Fe3+
) available, this mechanism could possibly be occurring. For example, the oxidation
of 1 mol of elemental sulfur coupled to the reduction of 6 mol of iron Fe (III) giving 6
mols of Fe (II) with the concomitant yield of 1 mol of sulfate, has previously been
described to occur in some strains of Thiobacillus ferroxidans 194
. In addition, the
oxidation of sulfur compounds has been observed when coupled to nitrate reduction 195
.
However, we do not support the latter, as no nitrate has been detected in these tailings.
In summary, the quantification of the specific genes involved in the metabolic
oxido-reduction of sulfur compounds and the production of methane, has helped us
corroborate the major microbial physiological processes ongoing in tailings ponds. In
particular, the association between Desulfocapsa and Thiobacillus seems to be playing
an important role in the sulfur metabolism and cycling in the tailings. More studies need
to be carried out regarding any putative ANME community members in the tailings,
thereby discerning the major CH4 cycling involved in oil sands tailings ponds.
150
Chapter Seven: The effects of substrates and alternate electron acceptors on
anaerobic microbial communites in oil sands tailings ponds
7.1 Introduction
It was discussed in Chapter One that naphtha, NA, or bitumen could potentially be
carbon sources1 in oil sands tailings ponds. Several studies regarding the use of naphtha
components such as alkanes and BTEX compounds have shown that methanogenic
communities in tailings ponds and other environments are able to thrive at their expense
41,47,68,69. Biodegradation of NAs by tailing pond microbes has also been carried out using
mainly commercially available NAs which can serve as surrogates to natural NAs 65
(see
Chapter Five). These studies have been carried out using tailings samples obtained
mainly from Syncrude operations or non-tailings sources. In contrast, the substrates used
by microbial communities in other tailings ponds (e.g., managed by other oil sands
operators) are poorly understood.
Therefore, using anaerobic samples from a Suncor tailings pond, we assessed the
effects of naphtha, NA, or bitumen as carbon sources on the tailings microbial
communities. We focussed mainly on the effects of these carbon sources under
methanogenic and sulfate-reducing conditions, as these physiologies are prevalent in the
Suncor tailings ponds [Chapter Four and Chapter Six]. In addition, the effects of nitrate
addition on tailings communities and on sulfate reduction and methanogenesis was
explained in the content of using an alternate densification reagents.
1 For simplicity, carbon and energy sources will be referred to as carbon sources
151
Understanding how hydrocarbon-degrading communities function in tailings ponds
due to the presence of various carbon sources and nutrients or electron acceptors can be
of significant importance to improve pond management.
7.2 Methods
7.2.1 Anaerobic enrichment to determine the effects of carbon sources for sulfate
reduction and methanogenesis in tailings ponds.
Enrichments were set up under sulfate reducing and methanogenic conditions,
using tailings as the microbial inoculum and NA, naphtha, or bitumen as the carbon
sources. Since tailings contain enough nutrients for the indigenous population to grow
and reproduce, several transfers were necessary before the effect of the various carbon
sources were assessed. Three transfers were accomplished in a period of a year and a
half.
Microbial inoculum:
The microbial inoculum was prepared from Suncor tailings pond 6 sampled in
2010, using the samples collected from 6 and 22 mbs. The selection of the depths was
based on distinct chemical profiles exhibited [Figure 4-8]. For instance, at 6 mbs the
highest concentration of sulfide was measured (0.5 mM) and at 22 mbs, sulfide
concentrations were among the lowest (0.1 mM) [Figure 4-8 (B)], suggesting that sulfate
reduction may be more important in incubations prepared from the 6 mbs sample than the
22 mbs sample.
152
The experiment started with a 5 mL pre-culture which was transferred (1 mL) after
45 days of incubation into 60 mL serum bottles containing Pfennig medium . The
successive transfers (5 mL) were done at approximately every 150 days, when sulfate
was totally consumed, and methane was produced in the negative controls (presumably at
the expense of residual tailings substrates). Figure 7-1 shows the appearance of the
bottles for each of the transfers.
Carbon sources:
Natural NA were extracted from tailings pond 6 surface water according to a
modification of the method of Holowenko et al., (2001) 32
and were distributed in
anaerobic serum bottles with Pfennig medium at a concentration of 20 mg · L-1 (0.3 %).
Naphtha, obtained from Plant 4 at Suncor, was used at 0.5 vol %. This substrate was
added together with 1 mL of heptamethylnonane to allow for slow release of naphtha into
the medium and to minimize toxicity. Finally, another set of experiments with bitumen,
extracted from oil sands using DCM, as the only carbon source, were prepared. Each
serum bottle was prepared with 15 mL of Pfennig medium [Table 3-8] supplemented
with 0.2 mL of vitamins [Table 3-10] and 5 mM of sulfate to the sulfate-reducing
enrichments only.
153
Experiment:
Table 7-1 summarizes the experimental design for the enrichments prepared from
the 6 and 22 mbs samples. For the first two transfers, the experiments had no replicates.
Only for the final set of experiments, was each condition prepared in triplicate. Bottles
were incubated in the dark at room temperature.
Methane formation (section 3.3.2.2) and sulfate depletion (section 3.2.3) were
measured every month. Microbial community composition was analyzed for each bottle
soon after the third transfer was initiated.
154
Figure 7-1 Appearance of enrichments after each transfer (done ~ every 150 days).
Notice how residual tailings are more visible in the first two transfers, but a small
amount still remains in the third transfer.
1st transfer 2nd transfer 3rd transfer
155
Table 7-1 Tailings enrichments amended with naphtha (0.5 vol %) or NAs (20 mg ·
L-1
) under methanogenic or sulfate-reducing conditions. Each condition was set up
in triplicate in 60 mL serum bottles that contained 15 mL Pfennig salts medium.
The microbial inoculum was from Suncor tailings pond 6 sampled in 2010 from 6 or
22 mbs.
6 mbs tailings enrichments 22 mbs tailings enrichments
Medium + sulfate + NA (6m) Medium + sulfate + NA (22m)
Medium + NA (6m) Medium + NA (22m)
Medium + sulfate + Naphtha (6m) Medium + sulfate + Naphtha (22m)
Medium + Naphtha (6m) Medium + Naphtha (22m)
Medium + sulfate (- control) (6m)
(no electron donor added)
Medium + sulfate (- control) (22m)
(no electron donor added)
Medium (-control) (6m)
(no electron acceptor added)
Medium (-control) (22m)
(no electron acceptor added)
156
7.2.2 Nitrate as an alternate electron acceptor in the presence of naphtha
Microbial inoculum and carbon source:
Tailings (10 g) from pond 5 sampled in 2010 (3 mbs) were used as the source of
microbial inoculum for determining the effect of nitrate on tailings microbial
communities. This depth showed the highest methanogenesis rate (0.4 nmol . cm-3
. day-
1) [Figure 4-15 (C)].
Naphtha (0.5 %) was used as the carbon source. It was distributed into 60 mL
serum bottles that contained 10 mL of Pfennig medium (supplemented with 0.2 mL
vitamines mixture [Table 3-10]) together with 1 mL of hepthamethylnonane. Sulfate and
nitrate were added at 5 or 10 mM final concentrations.
Experiment:
Table 7-2 summarizes the experimental bottles prepared for this part of the study.
Each experimental condition was set up in duplicate with a negative control for each
condition (tailings and medium, no substrate and no electron acceptor added). Bottles
were incubated in the dark at room temperature. Methane and sulfate concentrations were
measured by GC or HPLC as described in sections 3.3.2.2 and 3.2.3, respectively. Sterile
and non-sterile controls (tailings + naphtha, or tailings + medium) were also prepared.
The experiment covered a period of 256 days after which time the microbial communities
were analyzed by 454 pyrosequencing [Section 3.4.3].
157
Table 7-2 Tailings enrichment experiment using naphtha (0.5 %) as the carbon
source with nitrate and/or sulfate as the electron acceptors added at 5 or 10 mM.
The microbial inoculum was from pond 5 2010, 3 mbs tailings.
Enrichment SO4
2-
(5 mM)
SO42-
(10 mM)
NO3-
(5 mM)
NO3-
(10 mM)
tailings+naphtha+ medium
tailings+naphtha+ medium
tailings+naphtha+ medium
tailings+naphtha+ medium
tailings+naphtha+ medium
158
7.3 Results
7.3.1 Methane and sulfate in carbon source enrichments experiments
Figure 7-2 shows the results of the first, second, and third transfers on the carbon
sources tested under methanogenic conditions. Samples from 6 mbs showed an initial
preference for NA (after first transfer) [Figure 7-2 (A)] based on the amount of methane
produced. The experiments enriched with tailings from 22 mbs amended with naphtha,
produced the highest methane levels in the first transfer [Figure 7-3(B)]. During the first
and second transfers, methane produced in the experiments with both carbon sources
(NAs and naphtha) produced relatively low methane (~ 50 µmol), however, after the
third transfer, the experiments with tailings from 22 mbs amended with naphtha, peaked
to around 120 µmol of methane [Figure 7-2(B)]. After the third transfer, experiments
with 6 mbs tailings and naphtha showed higher methane production in comparison with
experiments with NAs for the same depth of tailings. However, methane production for
this depth was always lower than for the experiments with tailings from 22 mbs amended
with naphtha [Figure 7-2(B)]. The values of methane obtained from NAs added as a
carbon source at both depths were very similar to that of the negative control, where only
the bacterial inoculum (tailings) and medium were incubated. This suggests that methane
is coming from any background substrates present in the residual tailings rather than
from NA metabolism. Although less tailings was present in the serum bottles after the
third transfer, a small amount still remained [Figure 7-1]. Bitumen did not serve as
carbon source under methanogenic or sulfate-reducing conditions, as no methane was
produced or sulfate reduced from any of the experiments. For this reason, no sucessive
159
transfers were carried out for this substrate [Figure 7-2]. Under sulfate-reducing
conditions, similar results were obtained, in which sulfate was depleted in the first and
second transfers in the NA- and naphtha-amended bottles relative to controls (data not
shown).
160
Figure 7-2 Monitoring of methane production by enrichments amended with
naphtha or natural NAs to enrichments with tailings from 6 and 22 mbs from pond
6 2010. The arrows indicate each transfer.
0
20
40
60
80
100
120
140
0 100 200 300 400 500 600 700
CH
4(µ
mol
)
Time (days)
6 mbs
6m, NA
6m, Naphtha
6m (control)
6m, bitumen
0
20
40
60
80
100
120
140
0 100 200 300 400 500 600 700
CH
4 (µ
mol
)
Time (days)
22 mbs
22m NA
22m, Naphtha
22 m (control)
22m, bitumen
A
B
161
After 188 days of incubation following the third transfer, methane production and
sulfate depletion were observed when either NA or naphtha substrates were present
[Figure 7-3]. However, enrichments amended with naphtha showed more sulfate
reduction and methane production relative to the sulfate-free controls, especially when
the 22 mbs sample was used as the microbial inoculum [Figure 7-3(C, D)]. In these
enrichments, sulfate depletion started after 33 days of incubation and methane production
started to increase soon after 97 days [Figure 7-3 (C, D)]. With the 6 mbs sample, no
additional depletion of sulfate or production of methane was observed after 100 days of
incubation relative to the substrate-free controls [Figure 7-3 (A, B)].
The highest methane production was approximately 32 µmol and it was observed
in the samples collected from 22 mbs, while in the 6 mbs enrichments, only 3 µmol of
methane was produced after 188 days. No difference in methane production or sulfate
reduction in the naphtha or natural NA was observed when tailings originating from the 6
mbs was used as the microbial inoculum [Figure 7-3 (A, B)].
162
Figure 7-3 Methane production and sulfate depletion observed after the third
transfer of tailings enrichments with natural NA or naphtha as carbon sources
using samples collected from 6 and 22 mbs of Suncor Pond 5. (A) Sulfate depletion
for enrichments with tailings from 6 mbs; (B) methane production from
enrichments with tailings from 6 mbs; (C) sulfate depletion from enrichments with
tailings from 22 mbs; (D) methane production from enrichments with tailings
collected from 22 mbs. The error bars represent the standard error of 3 replicates.
0
1
2
3
4
5
6
7
8
0 50 100 150 200
Su
lfa
te (
mM
)
Time (days)
6 mbs
Medium + sulfate + NA (6m)
Medium + sulfate + Naphtha (6m)
Medium + sulfate (- control) (6m)
-5
0
5
10
15
20
25
30
35
0 50 100 150 200
Met
ha
ne
(um
ol)
Time (days)
6 mbs
Medium + NA (6m)
Medium + Naphtha (6m)
Medium (-control) (6m)
0
1
2
3
4
5
6
7
8
0 50 100 150 200
Su
lfa
te (
mM
)
Time (days)
22 mbs
Medium + sulfate + NA (22m)
Medium + sulfate + Naphtha (22m)
Medium + sulfate (- control) (22m)
-5
0
5
10
15
20
25
30
35
0 50 100 150 200
Met
ha
ne
(um
ol)
Time (days)
22 mbs
Medium + NA (22m)
Medium + Naphtha (22m)
Medium (-control) (22m)
A B
C D
163
7.3.2 Microbial community when different carbon sources are available in tailings
The microbial community profiles were examined following sulfate – amended or
sulfate - free incubations enriched on NA or naphtha from the 6 and 22 mbs microbial
communities following the third transfer. For the 6 mbs-derived enrichments, the
identified methanogens grouped under the genera Methanospirillum, Methanofollis, and
Methanobacterium were enriched, particularly when NA was used as the carbon source.
Methanospirillum was the most abundant genus reaching a maximum of 44 % of the
pyrosequencing OTUs when NA and sulfate were in the medium. When no sulfate but
NA were present (e.g. under methanogenic conditions), an abundance of only 25 % of
this methanogen was found [Figure 7-4] (A). The addition of naphtha as the sole source
of carbon enriched species related to Desulfobacter under sulfate reducing conditions,
but Thauera sp. were most abundant when sulfate was absent. Naphtha enrichments from
the 6 mbs samples also selected for the methanogens mentioned above but only at an
abundance of 4 % of the pyrosequencing OTUs [Figure 7-4 (A)]. Other genera refers to
approximately 40 different genera with abundance lower than 3% [Figure 7-4].
Enrichments prepared with tailings from 22 mbs showed a greater diversity than
those with 6 mbs. When NA and sulfate were present, organisms affiliating with
Acidaminobacter and Sediminibacterium were dominant, comprising 13% and 8% of
pyrosequencing OTUs, respectively. For this enrichment, methanogens grouped under
the genera Methanospirillum, Methanobacterium, and Methanosaeta at an abundance of
only 3 to 5 % of the pyrosequencing OTUs identified at the genus level. However, when
no sulfate was available, and NA was the only carbon source, 5 different methanogenic
164
genera (Methanospirillum, Methanofollis, Methanobacterium, Methanosaeta,
Methanolinea), were prominent along with bacteria grouped under Thauera and
Acidovorax.
165
Figure 7-4 Microbial community analysis of tailings enrichments from pond 5
(2010) samples identified at the genus level after the third tranfer of NA and
naphtha-amended enrichments. Naphtha and NA were used as sole carbon sources
under methanogenic or sulfate reducing conditions. (A) Enrichments prepared with
tailings from 6 mbs, (B) enrichments prepared with tailings from 22 mbs.
A
B
0 20 40 60 80 100
6 mbs, SO4, NA
6 mbs, CH4, NA
6 mbs, SO4, naphtha
6 mbs, CH4, naphtha
% of pyrosequencing OTUs
Methanospirillum
Methanofollis
Methanosarcina
Methanobacterium
Thauera
Desulfobacter
Geobacter
other genera
0 20 40 60 80 100
22 mbs, SO4, NA
22 mbs, CH4, NA
22 mbs, SO4, naphtha
22 mbs, CH4, naphtha
% of pyrosequencing OTUs
Methanospirillum
Methanofollis
Methanosaeta
Acidaminobacter
Methanosarcina
Methanolinea
Methanobacterium
Thauera
Acidovorax
Sediminibacterium
Desulfocapsa
Desulfobacter
Geobacter
Leptolinea
Flavobacterium
Citrobacter
other genera
166
For the naphtha- and sulfate-amended enrichments prepared with tailings from 22
mbs, species belonging to Leptolinea, Flavobacterium, Acidovorax and Citrobacter were
abundant. Also, methanogens affiliating with Methanosarcina, Methanosaeta, and
Methanolinea were relatively abundant. For this same depth (22 mbs), under
methanogenic conditions, different methanogens were found with the exception of
Methanosarcina. They included Methanospirillum, Methanofollis, and
Methanobacterium [Figure 7-4(B)].
In general, both carbon sources enriched for methanogenic Archaea and sulfate
reducers among other genera including Thauera and Geobacter. However, in the 22 mbs
enrichments, a more diverse population was present based on 454 pyrosequencing and
identifications at the genus level. For example, members of the genera Flavobacterium,
Acidovorax, Acidaminobacter, Sediminibacterium, and Citrobacter were in the 22 mbs
enrichments but not in the 6 mbs enrichments. Naphtha as a carbon source enriched both
methanogens and SRB in the presence or absence of sulfate.
7.3.3 Methane inhibition by nitrate
In addition to examining the potential for a variety of substrates to drive sulfate
reduction and methanogenesis, the effect of nitrate addition as an alternate electron
acceptor was also considered. Specifically, the effect of nitrate addition on methane
production and sulfate reduction was assessed. In these experiments, naphtha was added
as the carbon source because this carbon source appeared to be driving methanogenesis
and sulfate reduction in our previous experiments [Figure 7-3(C, D)].
167
The addition of naphtha improved the microbial activity in all the conditions tested
as the consumption of sulfate and nitrate was faster when naphtha was available [Figure
7-5 and Figure 7-6]. Little difference in the methane inhibition was observed between the
control with naphtha and the experiment with the different nitrate and sulfate additions.
However, methane was significantly inhibited when compared to the controls that had
none of these electron acceptors [Figure 7-5 and Figure 7-6].
In all the experiments, a lag phase of approximately 100 days was observed. After
this time, the methane production sharply increased in the experiments with no electron
acceptors [Figure 7-5 and Figure 7-6]. For experiments with only nitrate added, after 100
days of incubation, the nitrate was completely consumed in the 5 mM nitrate enrichments
or half way consumed in the 10 mM nitrate enrichments [Figure 7-5]. However, for these
experiments, the nitrite concentrations remained relatively constant for the same period
of time and the sulfate concentrations were also relatively constant [Figure 7-5].
In the enrichments where both sulfate and nitrate were added, nitrate was reduced
faster than the sulfate, specifically in the experiments amended with naphtha [Figure
7-6]. Sulfate reduction started to occur when nitrate had been completely depleted.
Interestingly, for these enrichments the concentration of nitrite increased 3 fold after 100
days and then remained constant. However, the nitrite concentration did not reach
stoichiometrically-expected amounts based on initial nitrate concentrations added [Figure
7-6]. The values of nitrate shown in the graphs are always a little bit above the initial
concentration added presumably due to interference in the HPLC measurements.
168
Figure 7-5 Enrichments with naphtha as the electron donor and nitrate or sulfate as
the electron acceptor. Methane, sulfate, nitrate, and nitrite levels in enrichments
containing (A) 5 mM nitrate, or (B) 10 mM nitrate. Error bars where visible,
represent the standard error of two replicates.
A B
0
5
10
15
20
0 50 100 150
NO
3-(m
M)
Time (days)
0
5
10
15
20
25
30
0 50 100 150
CH
4(u
mol
)
Time (days)
0
5
10
15
20
25
30
0 50 100 150
CH
4(u
mol
)
Time (days)
0.0
0.5
1.0
1.5
0 50 100 150
NO
2-(m
M)
Time (days)
0.0
0.5
1.0
1.5
0 50 100 150
NO
2-(m
M)
Time (days)
( ) 5mM NO3- + naphtha
(■) 5mM NO3-
( ) tailings + medium + naphtha
( ) 10mM NO3- + naphtha
(■) 10mM NO3-
( ) tailings + medium + naphtha
0
1
2
3
4
5
0 50 100 150
SO42-
(mM
)
Time (days)
0
1
2
3
4
5
0 50 100 150
SO42-
(mM
)
Time (days)
0
5
10
15
20
0 50 100 150
NO
3-(m
M)
Time (days)
169
Figure 7-6 Enrichments with naphtha as the electron donor and nitrate and sulfate
as the electron acceptor. Methane, sulfate and nitrate measurements in incubations
containing (A) 5 mM nitrate, 5 mM sulfate, (B) 10 mM nitrate, 5 mM sulfate, (C) 5
mM nitrate, 10 mM sulfate. Error bars where visible, represent the standard error
of two replicates.
0
5
10
15
20
25
30
0 50 100 150
CH
4(u
mol
)
Time (days)
0
5
10
15
20
25
30
0 50 100 150
CH
4(u
mol
)
Time (days)
0
5
10
15
0 50 100 150
SO42-
(mM
)
Time (days)
0
5
10
15
20
0 50 100 150
SO42-
(mM
)
Time (days)
0
5
10
15
0 50 100 150N
O3- (m
M)
Time (days)
0
5
10
15
20
0 50 100 150
NO
3-(m
M)
Time (days)
A
0
5
10
15
0 50 100 150
SO42-
(mM
)
Time (days)
0
5
10
15
0 50 100 150
NO
3- (mM
)
Time (days)
0
5
10
15
20
25
30
0 50 100 150
CH
4(u
mol
)
Time (days)
( ) 5 mM NO3- + 5 mM SO4
2- + naphtha
(■) 5 mM NO3- + 5 mM SO4
2-
( ) tailings + medium + naphtha
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150
NO
2-(m
M)
Time (days)
( ) 10 mM NO3- + 5 mM SO4
2- + naphtha
(■) 10 mM NO3- + 5 mM SO4
2-
( ) tailings + medium + naphtha
( ) 5 mM NO3- + 10 mM SO4
2- + naphtha
(■) 5 mM NO3- + 10 mM SO4
2-
( ) tailings + medium + naphtha
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150
NO
2- (mM
)
Time (days)
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150
NO
2-(m
M)
Time (days)
B C
170
7.3.4 Microbial community composition when nitrate is available
A genus-level survey of the microbial composition present in some of the nitrate-
amended enrichments is shown in Figure 7-7. In general, the addition of naphtha together
with the salts present in the minimal medium, enriched the microbial population
originally present at the beginning of the experiment (tailings, medium, t=0).
The most abundant sequences in all the experiments belonged to the genus
Thiobacillus with an average abundance of 12% of the pyrosequencing OTUs. The most
prominent methanogens affiliated with Methanosaeta and Methanolinea, comprising on
average 7.4 and 2.4 % of the pyrosequencing OTUs, respectively. Both methanogenic
activity was greatly inhibited in enrichments with 5 mM NO3- and 10 mM SO4
2-, and in
enrichments where 10 mM nitrate and naphtha were available [Figure 7-7]. Regarding
the sequences affiliating with SRB, the most abundant were Desulfuromonas sp. and
Desulfocapsa sp. with 3.5 and 1.2 average % of pyrosequencing OTUs, respectively. The
latter was more enriched (5 % of pyrosequencing OTUs) in the 5 mM NO3- + 10 mM
SO42-
+ naphtha enrichments. Known syntrophic or hydrocarbon-degrading bacteria, such
as Smithella and Brachymonas were also detected in all the enrichments [Figure 7-7]. In
particular, Smithella sp. was markedly abundant in the experiment where no alternate
electron acceptor was supplied, comprising 12.7 % of the pyrosequencing OTUs. Other
genera represents approximately 130 different genera with abundance lower than 3 %
[Figure 7-7].
171
Figure 7-7 Percentage of pyrosequencing OTUs present in tailings enrichments with
no added electron acceptor or with nitrate and/or sulfate added as electron
acceptors. Other genera represent % of pyrosequencing OTUs < 3 % of the total
community identified at the genus level.
0 50 100
10 mM nitrate naphtha
10 mM nitrate
5 mM nitrate 10 mM sulfate naphtha
5 mM nitrate 10 mM sulfate
10 mM nitrate 5 mM sulfate naphtha
10 mM nitrate, 5 mM sulfate
tailings, medium, naphtha
tailings, medium
tailings, medium t=0
% of pyrosequencing OTUs
Thiobacillus
Methanosaeta
Methanolinea
Desulfuromonas
Desulfocapsa
Leptolinea
Smithella
Brachymonas
Acinetobacter
other genera
172
7.4 Discussion
7.4.1 Naphtha vs. natural NAs vs. bitumen as electron donors for anaerobes in tailings
ponds
The presence of less than 1% of naphtha, 40 to 70 mg ·L-1 of NAs, and 3% of
residual bitumen in tailings ponds suggests that these compounds are the most likely
available carbon and energy sources for the microbial population in the ponds. Naphtha
has previously proved to support methanogenesis 41,47,68,69
and NAs have shown to be
biodegradable aerobically depending on the chemical properties of the acids 34,64-
67,145,149,151,166. In the present study, bitumen was initially set up as a carbon source but
since no microbial growth was detected during the first incubation period [Figure 7-2],
the initial incubations were not successively transferred. The current study thus focussed
on investigating the preference for natural NAs and/or naphtha in enrichments prepared
from two distinct depths of tailings samples from Suncor Energy Inc. (Pond 6 2010
samples).
The microbial community composition enriched with NA or naphtha varied likely
due to the presence of different substrates. The 454 pyrosequencing of the enrichments
prepared with these two carbon sources gave rise to species related to the spiral shaped
H2 – CO2 and formate utilizing Methanospirillum 196
as the most abundant taxon [Figure
7-4], in particular for tailings collected from 6 mbs with NAs as the sole source of
carbon. However, the 454 pyrosequencing of the native microbial composition of pond 6
2010 at 6 mbs and 22 mbs (e.g. unenriched), did not reveal the presence of the genus
173
Methanospirillum in any of the depths sampled (3 – 22 mbs) [Chapter Four:]. This
confirms that current technology to detect or quantify microorganisms from the
environment has its limitations and we can mainly detect what we select for in the first
place. Thus, we can infer that Methanospirillum sp. was always present in tailings but at
a very low abundance, not detected by our DNA extraction and amplification protocols.
However, when macro- and micronutrients were supplied (by the basal salt medium
components), members of this genus were able to proliferate.
In all of the naphtha or NA-amended enrichments, the methanogenic members
were more abundant than the SRB, even in the bottles amended with SO42-
. Considering
that DNA was extracted soon after the third transfer had started, this result was somewhat
expected. Since each successive transfer was done when the sulfate from the previous
culture was depleted, and when the un-amended controls had started to produce methane,
selection for the methanogenic population was probable. Interestingly, in all the
conditions, at least one known sulfate reducer (Desulfobacter and/or Desulfocapsa), a
hydrocarbon degrader (possibly Thauera), and several methanogens (Methanospirillum,
Methanofollis, Methanosarcina, Methanobacterium, Methanolinea, Methanosaeta) were
present. This is similar to a result published by Ficker et al (1999) who examined
microbial community composition in an anaerobic toluene-degradng culture 197
. In a 10-
year experiment, they observed that in a methanogenic consortium enriched with material
from a creosote-contaminated aquifer and maintained with toluene as the sole source of
carbon, two methanogenic Archaea (Methanosaeta and Methanospirillum) together with
a sulfate reducer (Desulfotomaculum) and a bacterium not related to any previously
174
described genus were associated with the degradation of toluene 197
. Similarly, Ulrich
and Edwards 198
obtained a mixed community of sulfate reducers, methanogens and
syntrophs in an anaerobic culture amended with benzene as the source of carbon. They
suggested that one of the bacteria may be responsible for the toluene or benzene attack,
generating partially oxidized products such as fatty acids or alcohols that become
available for the other bacteria (presumably the SRB acting as a fermenter) that would
further degrade these low molecular weight compounds into acetate, CO2 and H2. Lastly,
methanogens would complete the degradation pathway to CO2 and CH4 197,198
. From our
results, we can speculate that Thauera sp. may be an important primary hydrocarbon
degrader while Desulfobacter sp. and/or Desulfocapsa sp. are acting as syntrophs
providing the small molecular weight compounds for the hydrogenoetrophic
(Methanospirillum) or acetoclastic methanogens (Methanosaeta). Thauera sp. are well
known for their capability of growing with toluene as the sole source of carbon under
nitrate-reducing conditions. Some members of this genus carry out the fumarate addition
reaction, a common mechanism in anaerobic degradation 199
. It is not clear why an
organism known mainly for nitrate reduction would become enriched in a methanogenic
enrichment from tailings ponds. However, Thauera species have previously been
reported to be present in oil sands tailings ponds 38,40
, in industrial wastewater treatment
plants 200
, and in an Alberta oilfield where methanogens also dominate 201
.
The differences in the microbial community composition obtained in our cultures
enriched from 6 mbs and 22 mbs zones, confirms the microbial heterogeneity of the
tailings ponds as well as the metabolic variety observed in these complex ecosystems.
175
Interestingly, the samples collected from the deeper depth were more diverse. At 22 mbs,
we identified many putative naphtha degraders such as Flavobacterium sp. 163,202
,
Acidovorax sp. 130,131
, Acidaminobacter sp. 203
, and Citrobacter sp. 204
that were not
detected at 6 mbs. These bacteria may well be associated in syntrophic interactions with
the methanogens that were also prevalent. Among them, the H2- and CO2 -utilizing
Methanospirillum sp. and Methanofollis sp. were the most dominant in all the conditions.
Previous studies have detected these Archaeal groups in hydrocarbon-associated
environments 140,205
. Organisms affiliated with Methanosaeta, Methanolinea, and
Methanobacterium were also naturally found in the tailings ponds [Chapter Four], and
have been previously enriched in laboratory incubations containing hydrocarbons 39,69
.
Other bacteria like Sediminibacterium sp. (previously detected by molecular techniques
from a uranium mine 206
) may also be contributing to the degradation of hydrocarbon
substrates however not much literature is available regarding this genus.
Overall, under enrichment conditions, there seems to be a preference for naphtha
over NA by anaerobic tailings microbial populations as a carbon source, both under
methanogenic and sulfate reducing conditions [Figure 7-3]. Initially, enrichments
prepared from 6 mbs samples appeared to be less inhibited by NA than by naphtha
(based on methane production, sulfate reduction) but after the third transfer naphtha was
favoured, as enhanced methane production and sulfate consumption was observed
relative to the controls. In the NA-amended enrichments, methane production and sulfate
reduction were not enhanced relative to the controls [Figure 7-2]. It is possible that in the
first transfers, the microbial population was living more at the expense of residual
176
hydrocarbon compounds attached to the clay particles. As the tailings were diluted with
the successive transfers, the substrates were no longer available hence the microbial
community was potentially limited by carbon sources and not able to utilize the supplied
natural NAs. Even under aerobic conditions, degradation of natural NAs has been shown
to be more difficult than model and commercially available NAs 207
due to their complex
chemical structure (branched alkyl chains), the range number of compounds present in
naturally occuring samples83,149
, as well as their toxicity and surfactant properties 36
.
However, Herman et al. 65,67,146
have demonstrated that microorganims from oil sands
tailings have the potential to degrade both alkyl side chain and carboxylated cycloalkane
ring components of NAs but the rate at which the degradation occurs seems to be
affected by the limitation of nitrogen and phosphorous and such activity is under aerobic
conditions. It is most likely that more incubation time is needed before we see a marked
depletion of these compounds under energetically less favored anaerobic conditions.
On the other hand, biodegradation studies with naphtha 47
, typically comprising a
mixture of short chain alkanes 41
, long chain alkanes from bitumen components 68
, and
monoaromatic compounds have previously been conducted under methanogenic
conditions with endogenous microbial populations from Syncrude Canada Ltd. tailings
ponds. The results showed that the methanogenic communities are capable of degrading
these compounds in the order of C10 >C8 > C7 > C6 47
. Similarly, longer chain alkanes
(C14, C16, and C18) were also completely degraded although longer incubation times were
needed (440 days) with longer adaptation phase (180 – 280 days) before any methane
production occurred compared to the degradation of short chain alkanes ( 10 days) 68
.
177
BTEX compounds were also found to drive methane production in tailings enrichments
47. Our results confirm that naphtha components are serving as key carbon substrates in
Suncor tailings ponds. Although naphtha compounds were not measured, our enrichment
studies showed significantly enhanced levels of methane production and sulfate reduction
when whole naphtha was supplied relative to controls, suggesting that the degradation of
naphtha was driving these processes. Figure 7-8 shows an overview of which species
were enhanced when naphtha was available in comparison to species found naturally in
tailings pond 6.
178
Figure 7-8 Microbial processess in Suncor oil sands tailings pond 6 2010. (A)
unamended tailings, (B) naphtha-amended tailings. The microbial genera were
identified using 454 pyrosequencing and only the most abundant taxa are presented.
Unenriched tailings
Available naphtha
Partially oxidized
compounds
H2, CO2,
formate,
acetate
CH4
Pseudomonas
Acinetobacter
Desulfocapsa
Methanosaeta
Methanolinea
SO42-
HS-
sulfite
SO42-
Fe3+
Fe2+
Thiobacillus
Desulfocapsa
HS-
Other processes
Naphtha
Partially oxidized
compounds
H2, CO2,
formate,
acetate
CH4
Thauera
Desulfocapsa
Desulfobacter
Methanosaeta
Methanospirillum
Methanofollis
Methanosarcina
Methanobacterium
Methanolinea
SO42-
HS-
Naphtha Enrichment
A B
Syntrophus
179
7.4.2 Nitrate as an alternate electron acceptor in tailings ponds
The addition of gypsum to tailings ponds to enhance solids sedimentation (e.g. in
CT operations) has the drawback of supplying sulfate to SRB with the concomitant risk
of producing hydrogen sulfide. Under typical tailings conditions, only around 3 % of the
total sulfide is expected to escape to the surface as H2S gas, due to the alkalinity of the
tailings 16
. At pH 7 – 8, most of the sulfide is present as HS-, which has a tendency to
precipitate as iron and other metal sulfides 16
. Substituting gypsum with calcium nitrate
to enhance tailings sedimentation rates, and to avoid the production of sulfide, could be
considered by the oil sands operators as an alternative pond management practice if
sulfide emissions become an issue in the area.
Nitrate reduction produces a higher energy (G’) than sulfate reduction as its
reduction potential is more positive. Therefore, in anaerobic systems bacteria can gain
more energy in transferring electrons when nitrate is available. Thus, as the reduction of
NO3-/ NO2
- has a E’0 = + 0.4 volts whereas SO4
2-/ HS
- only has a E’0 = 0.2. Volts. If
G’ = nFE0’, nitrate reduction would yield more energy to the bacteria than sulfate
reduction 54
. Further, nitrate reduction would be expected to inhibit methanogenesis.
In our experiments, the addition of nitrate at 5 or 10 mM together with sulfate at
similar concentrations was tested. The rationale behind this experimental design was to
determine whether there would be a shift in the inhibition of methane, currently occuring
by SRB when sulfate is available, to heterotrophic nitrate-reducing bacteria (hNRB) if
nitrate were to be added to tailings [Figure 7-9].
180
Figure 7-9 Schematic representation of the displacement of SRB by hNRB when
nitrate is available in tailings ponds.
181
As was expected, methane production was inhibited by the addition of nitrate
and/or sulfate [Figure 7-5 and Figure 7-6] to enrichments. The inhibition correlated with
a decrease in the relative abundance of syntroph Smithella, and/or a decrease in the
abundance of the methanogens Methanosaeta and Methanolinea; especially when 10
mM sulfate and/or 10 mM nitrate were added to the medium [Figure 7-7]. It is well
known that methanogens need small molecular weight compounds in order to carry out
their metabolism (e.g. acetate, formate, H2/CO2) and that these compounds are supplied
by the syntrophs 116
. The abundance of Smithella sp. in our cultures indicates that these
bacteria may be involved in the degradation of hydrocarbon (naphtha), producing
substrates for the methanogens. Siddique et al. 69
also detected Smithella sp. in
association with Syntrophus sp. in methanogenic cultures amended with naphtha and
BTEX. They attributed the presence of this association to the initial anaerobic activation
of alkanes and/or subsequent beta-oxidation of their metabolites to acetate 69
. Similarly,
Smithella was among some of the dominant species in an oil reservoir treated with nitrate
to control souring 201
, and in an alkane-degrading methanogenic culture enriched from
river sediments 106
. In our tailings enrichment cultures, the abundance of this genus in the
control (tailings + naphtha + medium), together with Syntrophus sp. and Leptolinea sp.
(2.0 average % of pyrosequencing OTUs) and the methanogens, suggests the
interconnection among them when no sufficient electron acceptor is around. However,
the addition of nitrate and sulfate causes shifts in the community, inhibiting the
methane/syntrophic association (e.g. genera associated with these activities decreased in
abundance) while enriching for Thiobacillus sp. [Figure 7-7].
182
In Chapter Six, the metabolic versatility of Thiobacillus sp. was discussed. In
particular, the denitrifying chemolithotroph Thiobacillus denitrificans, a bacterium
capable of reducing nitrate with ferrous iron 193,208
and FeS 209
as electron donors.
Equation 5 describes the oxidation of pyrite when nitrate is available, completely
reducing nitrate to N2 gas (a) or incomplete reduction to nitrite (NO2-) (b)
195.
Equation 5 Pyrite oxidation under nitrate reduction conditions
Thiobacillus, originally present in the tailings samples at time zero [Figure 7-7],
was enriched in all the experiments where either nitrate or sulfate was added,
independently of the presence of naphtha. This suggests that the predominance of this
microorganism in tailings (e.g. also observed in pond 5 and 6 samples, Chapter Four)
does not rely on naphtha as electron donor but instead it is likely using FeS2 (Fe(II) or
reduced S compounds) in tailings as the electron donor (refer to Appendix Twelve: for
Fe(II) values). Since no difference was seen in the % abundance of Thiobacillus when
only nitrate or nitrate/sulfate was added, we hypothesize that members of this genus are
either using reduced nitrate compounds as electron acceptor or sulfur compounds as
electron donors. Based on the stoichiometry of the reduction of nitrate to nitrite, and the
results obtained, we can infer that the added nitrate was either assimilated or completely
reduced to NO, N2O or N2 gas (denitrification) by Thiobacillus. Since the nitrite
concenrations did not vary during the whole incubation time in enrichments amended
FeS2(s) + 3NO3-
(aq) + 2H2O Fe(OH)3(s) + 2SO42-
(aq) + 1.5N2 (g) + H+ ∆G’ = 2439 kJ/mol (a)
FeS2(s) + 7.5NO3-(aq) + 3.5H2O Fe(OH)3(s) + 2 SO4
2-(aq) + 7.5NO2
-(aq) + 4H+ ∆G’ = 1954 kJ/mol (b)
183
with nitrate, we can infer that as nitrite was formed, it was rapidly reduced by
Thiobacillus [Figure 7-5]. In contrast, in enrichments amended with both sulfate and
nitrate, nitrite concentrations did increase during the incubation time [Figure 7-6]. When
sulfate is available, SRB can reduce these compounds to sulfide which can then be used
as electron donors by Thiobacillus while reducing nitrate 210
. Therefore, microbes present
in these enrichments could potentially use naphtha or reduced sulfur compounds as
electron donors while reducing nitrate, thus allowing for the accumulation of nitrite
[Figure 7-6]. Figure 7-10 shows an overview of the proposed metabolic processes in
these enrichments.
Either way, the reduction of nitrate can possibly lead to the production of NO and
N2O. These compounds can have detrimental consequences to the environment as their
accumulation can lead to ozone layer deterioration and the production of acid rain (as
nitric acid) 54
.
In summary, the addition of nitrate to tailings ponds could be used as an alternative
to inhibit methane production but the denitrification products could represent a higher
environmental risk than hydrogen sulfide produced from the reduction of sulfate. Future
studies should examine the production of these potentially harmful byproducts.
184
Figure 7-10 Proposed model of microbial community shifts when nitrate and/or
sulfate is added as alternate electron acceptors to tailings (pond 5 2010) amended
with naphtha. Left panel, no added electron acceptors showing increased average
abundance of Smithella and methanogens and lower abundance of Thiobacillus and
SRB. Right panel, when nitrate and/or sulfate added, lower average abundance of
Smithella and methanogens, and increased abundance of Thiobacillus and SRB.
No added electron acceptors
Naphtha
CH4 + CO2
Naphtha (+ 5 mM NO3- & 10 mM SO4
2-)
Partially oxidized
compounds
CO2
Desulfocapsa (0.9%)
Desulfuromonas (4.5%)
Methanosaeta (10.6%)
Methanolinea (5.6%)SO4
2-
HS-
Nitrate- or sulfate-treated tailings
A B
SO42-
NO3-
Thiobacillus
HS- NO2-
Other processes
NO3-
Thiobacillus
Fe2+ NO2-
Fe3+
NO3-
Thiobacillus
Naphtha NO2-
CO2
Smithella (0.2%)
Brachymonas (0.6%)NO3
-
NO2-
Smithella (12.7%)
Brachymonas (0.6%)
H2, CO2, formate, acetate
Thiobacillus (20.1%)Thiobacillus (4.1%)
Methanosaeta (2.5%)
Methanolinea (0.6%)
Desulfocapsa (0.6%)
Desulfuromonas (3.4%)
185
Chapter Eight: Conclusions
At the start of this thesis work, it was hypothesized that changes to tailings pond
management operations would result in a shift in the pond microbial communities and
activities based on changes in selective pressures to which the microbial communities
were exposed. For example, it was hypothesized that the addition of calcium sulfate
(gypsum) inhibits methanogenesis, and that as a pond ages, methanogens will dominate
the microbial community due to the lack of alternate electron acceptors, hence increasing
the probability of producing methane emissions. It was also hypothesized that pond
closure (e.g. a scenario where no new tailings or treatments are added to a tailings pond)
can potentially shift the microbial community composition and activities, but the
outcome was not known (e.g. does pond closure lead to positive or negative effects?).
Thus, gaining information about the key microbial players and activities that occur in
tailings ponds subject to different management strategies can help operators predict
whether certain operations will lead to desired (e.g. biodegradation/bioremediation of
tailings chemicals) or undesired effects (e.g. gas emissions).
To address the hypothesis, the microbial communities and physiologies in oil sands
tailings ponds were determined using samples collected from two tailings ponds being
operated using different management approaches. These parameters were monitored in
an active pond that was treated with gypsum (Suncor pond 6) and in another tailings
pond (also treated with gypsum) before and after closure (designated as an inactive pond,
Suncor pond 5). In order to thoroughly investigate microbial communities and activities
over time, depth-dependent sets of samples were collected and analyzed from the years
186
2008 to 2011. A variety of chemical analyses, microbial activity assays, microbial
community composition analyses, functional gene studies, and substrate determinations
were performed. The anaerobic microbial community composition together with their
main metabolic activities (sulfate reduction and methanogenesis rates), and the
quantification of the gene copy number for the genes involved in these reactions were
evaluated and compared. In order to determine the preferred substrate for anaerobic
tailings ponds communities, enrichments were established with different substrates
(bitumen, naphtha, or NAs) and methane production and sulfate reduction were
monitored along with an examination of the microbes presumably involved in consuming
the substrates. The microbial community composition and activities at the pond surface
were also assessed to examine the potential for aerobic surface microbes to use gases that
can potentially be emitted (e.g. H2S) and pure cultures were isolated and studied for their
ability to degrade NAs which are a source of known toxicity in tailings ponds.
The microbial community analysis in the active pond (pond 6) showed that the
main groups of organisms inhabiting the anaerobic depths comprise, in order of
abundance, the phyla Proteobacteria, Euryarchaeota, Chloroflexi, and Firmicutes, with
the first two phyla dominating (each comprising around 30 % of the average of
pyrosequencing OTUs). It was observed that these proportions change depending on the
management of the pond. For example, for the inactive pond (pond 5) prior to closure,
Proteobacteria comprised approximately 70% of the total OTUs while Euryarchaeota
comprised ~26 % of the average of pyrosequencing OTUs. However, after a year of no
tailings inputs, Proteobacteria abundance increased slightly to 77%, while Euryarchaeota
187
abundance decreased by approximately half (down to 12% of the total average
pyrosequencing OTUs). Similarly, at the genus level, the active pond (pond 6) harboured
methanogens as the major microbial groups whereas for the inactive pond (pond 5, after a
year following closure) a shift from a primarily methanogenic community to one more
dominated by putative hydrocarbon degraders was observed.
The 454 pyrosequencing of the 16S rRNA genes and the qPCR analysis of specific
functional genes indicated that the methanogens most commonly found in these tailings
ponds were Methanosaeta sp. and Methanolinea sp. In the active pond (pond 6), the
abundance of these methanogens closely paralleled that of Syntrophus sp. that were also
identified by 16S rRNA gene analysis, suggesting that syntrophic reactions are prevalent
in the tailings ponds, likely functioning to degrade carbon substrates to methane. This
observation supports previous findings in a Syncrude tailings pond and in other
hydrocarbon-degrading environments 68,69
. Microbial community analysis also showed
the dominance of 16S rRNA gene sequences associated with Desulfocapsa sp. and
Thiobacillus sp., organisms that are well known to be involved in sulfur metabolism.
Thiobacillus sp. are metabolically versatile in that they can be involved in reactions
involving sulfite oxidation, sulfate reduction, iron oxidation, iron reduction, and nitrate
reduction. Based on the finding of these two organisms in parallel, it is speculated that a
close commensalistic interaction is taking place between these two groups of bacteria.
Other organisms revealed by 16S rRNA gene sequencing that may be possibly playing
important roles in the biodegradation of hydrocarbon-like compounds in tailings ponds
188
include members of the genera Acinetobacter and Pseudomonas that were found in all
tailings samples.
The qPCR analysis targeting the dsrB gene correlated well as a function of depth
with the sulfate reduction rates and 16S rRNA gene sequencing results revealing the
abundance of SRB like Desulfocapsa. Interestingly, the sox genes also correlated
positively as a function of depth with the sulfate reduction rate and with the abundance of
Thiobacillus. However, the sox genes were not detected near the pond surface, where
aerobic sulfide oxidation is expected to occur and where laboratory experiments showed
slightly higher rates of sulfide oxidation in live tailings tests (e.g. biotic tests) compared
to sterile tailings tests (e.g. abiotic tests). These data suggest that abiotic sulfide oxidation
is more prevalent than biological sulfide oxidation near the pond surface to help prevent
sulfide emissions from the pond. The qPCR data for methanogens (e.g. quantifying the
mcrA gene) did not correlate as well with the methanogenic Archaea obtained by 454
pyrosequencing of the 16S rRNA gene. It was speculated that this may be related to the
presence of mcrA that can also be found in anaerobic methane oxidizers which may be
present in tailings based on other studies 187
. More studies regarding this idea need to be
carried out.
The surface water contained a completely different microbial community
composition in comparison to the anaerobic layers which was not unexpected given the
availability of oxygen as an electron acceptor at the surface, but not at depth. The tailings
pond microorganisms found at the pond surface are dominated by genera that have been
previously found to degrade hydrocarbons or that are metabolically associated with
189
algae. In a small proportion, sulfide oxidizers can also be found. Three isolates were
obtained from tailings pond surface water that are able to effectively degrade model NA
compounds, which shows that organisms at the tailings ponds surface may be able to
metabolize some carbon substrates added to the ponds following bitumen extraction.
These isolates can now be used as model organisms to study the biodegradation of NA in
more depth (such as for determining key enzymes and genes involved in the NA
metabolic pathways). Among the isolates obtained, some have been reported as aerobic
sulfide oxidizers (Xanthobacter sp.), although this process does not appear to be
operating in the ponds based on the studies conducted here. As mentioned earlier, if
sulfide reaches the surface due to sulfate reduction occurring at depth, it will most likely
be chemically converted to a more oxidized form.
The preference in substrate utilization by the anaerobic microbial populations in
tailings ponds seem to be more directed towards naphtha than to NAs as more microbial
activity was observed in cultures amended with naphtha than with NAs. Bitumen did not
serve as a carbon source under the anaerobic conditions tested. A common pattern of a
sulfate reducer, a methanogen, and a hydrocarbon degrader was seen in all the
enrichments confirming the cooperation among the species to degrade complex organic
compounds.
The effectiveness of nitrate as an alternate electron acceptor to inhibit
methanogenesis if sulfide emissions are ever an issue was also shown. However the fate
of the final products of denitrification is not known and could be deleterious to the
environment if nitrous oxides are produced. Interestingly the genus most enriched under
190
nitrate-amended conditions was Thiobacillus, which suggests the importance of this
group of bacteria in tailings ponds, specifically due to their versatile metabolism
associated with sulfur and iron. Through these studies, this genus has emerged as a major
microbial player in oil sands tailings ponds that can play an important role in many
metabolic processes, thus further studies targeting these bacteria is warranted.
Comparing the two ponds studied, we can conclude that for the active pond,
microbial activity was found throughout the depths studied (first 22 mbs), whereas for
the inactive pond, most of the microbial activity was concentrated closer to the surface.
However, a significant reduction of microbial activity was observed after pond 5 was
dewatered and closed. Sulfate reduction activity in the active pond (pond 6) was also
decreased due to a reduction of tailings inputs. The phylogenetic relationships between
all of the samples taken from both ponds under study showed that each pond, and each
sampling time are not closely related to each other, supporting the hypothesis that
changes in pond management can dramatically alter the community structure and thus
key activities in tailings ponds. However, the results herein obtained cannot yet be
generalized to other tailings ponds until further studies are conducted with other tailings
ponds (e.g. microbial monitoring studies of another pond undergoing closure) showing
similar shifts in microbial community composition and activities.
In summary, tailings ponds harbours a wide variety of microorganisms that likely
interact to carry out a variety of processes including sulfur metabolism, methane
production, and biodegradation both aerobically and anaerobically. Other processes like
nitrate and iron reduction can also occur as the tailings contain the microbes with genetic
191
capabilities to support these metabolic processes. The abundance and spatial distribution
of microbial communities is closely related to the substrate availability, which can vary
depending on the implemented pond management strategy. Therefore, the microbial
study of oil sands tailings ponds should not be underestimated and should be followed
carefully by operators in the oil sands region as part of the pond monitoring routine, both
to prevent negative environmental damage and/or to predict the outcome of a
management scheme.
192
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Appendix One: List of primers used for 16 S rRNA gene amplification
Primer Sequence (5’ 3’) references
1392r ACGGGCGGTGTCTRC 152
27f AGAGTTTGATCCTGGCTCAG 152
454 T-FB adaptor sequence of CTATGCGCCTTGCCAGCCCGCTCAG. 55
454 T-RA adaptor sequence of CGTATCGCCTCCCTCGCGCCATCAG 55
926f AAACTYAAAKGAATTGACGG 152
341f CCTACGGGAGGCAGCAG 211
534r ATTACCGCGGCTGCTGGCA 212
208
Appendix Two: Microbial rank identified in pond 6
Table 0-1 Microbial rank identified in pond 6 2008
#groupName
2
mbs
5
mbs
6
mbs
8
mbs
9
mbs
11
mbs
12
mbs
14
mbs
15
mbs
17
mbs
18
mbs
#totalCount 2860 6402 6296 6905 5581 3606 4937 3767 4855 5665 4980
#taxonomic term % % % % % % % % % % %
Archaea;Euryarchaeota;Methanomicrobia; Methanosarcinales;:Methanosaetaceae; Methanosaeta 50.6 16.8 16.8 23.2 17.1 18.8 20.8 14.0 20.1 9.7 14.0
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Candidatus _Methanoregula; 23.4 12.1 8.7 14.7 12.1 11.6 12.5 6.1 9.8 4.8 7.4
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;uncultured; 0.3 6.0 5.7 5.4 5.6 5.8 6.1 6.3 6.3 5.6 6.9 Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanolinea; 8.8 7.9 8.5 7.3 4.0 3.6 3.5 1.8 2.7 1.2 2.1
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Syntrophus; 0.2 5.1 7.1 7.1 3.4 1.7 2.8 2.1 2.7 1.4 3.1
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;Leptolinea; 0.4 3.5 2.7 3.3 3.1 3.0 3.0 3.0 3.8 2.5 3.1 Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobulbaceae;Desulfocapsa; 0.3 2.2 1.1 2.1 4.3 3.6 4.1 6.9 3.2 1.3 1.7
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;Thauera; 0.3 1.5 2.8 1.3 3.6 3.3 1.6 4.2 1.6 2.6 3.0
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Smithella; 0.1 4.7 4.2 3.3 3.6 3.0 2.4 1.0 2.0 0.4 0.6 Bacteria;Proteobacteria;Betaproteobacteria;Hydrogenophilales;Hydrogenophilaceae;Thiobacillus; 0.0 0.1 1.1 0.0 0.1 0.0 0.1 13.1 1.1 3.8 2.9
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Brachymonas; 0.0 0.1 0.6 0.1 0.1 0.1 0.0 0.7 2.3 7.8 10.1
Bacteria;Firmicutes;Clostridia;Clostridiales;Peptococcaceae;Pelotomaculum; 0.1 1.1 0.4 0.7 2.0 5.0 5.1 2.4 3.7 0.3 0.5 Bacteria;Actinobacteria;Actinobacteria;subActinobacteridae;Actinomycetales;subMicrococcineae; 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.1 16.7 1.8
Bacteria;Bacteroidetes;Sphingobacteria;Sphingobacteriales;vadinHA17; 0.1 1.7 1.7 2.2 1.8 2.0 1.8 1.8 1.9 1.2 1.8
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Acidovorax; 0.8 1.0 3.5 0.5 0.6 0.7 0.3 1.4 0.8 4.0 4.1 Bacteria;Candidate_division_WS6; 0.9 1.7 1.1 1.3 1.4 1.2 1.9 1.1 1.2 0.9 0.8
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae; 1.1 1.5 1.1 1.0 1.5 1.0 0.6 0.9 0.9 1.7 1.9
Bacteria;Spirochaetes;Spirochaetes;Spirochaetales;Spirochaetaceae;uncultured; 0.0 1.1 1.3 1.1 1.6 1.8 1.3 2.1 1.4 0.5 0.9 Archaea;Euryarchaeota;Thermoplasmata;Thermoplasmatales;AMOS1A-4113-D04; 0.6 0.8 1.3 1.0 0.5 1.3 1.2 1.0 2.4 0.6 1.8
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Rhodoferax; 0.1 0.7 2.5 0.9 1.3 1.4 1.2 0.7 1.0 1.4 1.4
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;uncultured; 0.1 1.7 1.1 1.4 1.7 1.1 1.5 1.0 1.4 0.4 0.9 Archaea;Euryarchaeota;Methanomicrobia;Methanosarcinales;Methanosarcinaceae;Methanomethylovorans; 0.3 0.2 0.3 0.2 0.3 0.3 0.6 1.2 1.1 5.6 1.2
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobacteraceae; 0.1 0.7 0.3 0.9 1.5 1.4 1.5 1.6 2.0 0.4 0.9
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobulbaceae;Desulfurivibrio; 0.1 1.0 0.3 0.5 2.3 3.5 2.0 0.4 0.7 0.1 0.2 Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae;Pseudomonas; 1.5 0.8 3.3 0.3 0.4 1.0 0.4 0.7 0.2 0.8 1.4
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfuromonadales;Geobacteraceae;Geobacter; 0.1 0.8 0.8 1.0 1.7 1.7 1.5 0.7 0.6 0.2 0.2
Bacteria;Firmicutes;Clostridia;Clostridiales;Peptococcaceae; 0.4 0.9 0.3 0.4 0.9 2.4 1.9 1.0 0.9 0.1 0.1 Archaea;Euryarchaeota;Thermoplasmata;WCHA1-57; 1.2 1.2 0.8 0.9 0.8 1.0 0.9 0.7 0.9 0.4 0.5
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;uncultured; 0.0 0.1 0.4 0.1 0.1 0.0 0.0 1.7 0.2 2.9 3.6 Bacteria;Proteobacteria;Betaproteobacteria; 0.1 0.1 0.7 0.0 0.0 0.0 0.1 2.2 0.5 2.2 3.1
Bacteria; 0.1 0.5 0.6 0.6 0.7 1.0 0.9 0.9 1.7 0.4 0.5
209
Table 0-2 Microbial rank identified in pond 6 2010
#groupName 3 mbs 6 mbs 9 mbs 12 mbs 15 mbs 18 mbs 21 mbs 22 mbs
#totalCount 7600 5379 6287 6012 6880 5880 7242 7030
#taxonomic term % % % % % % % %
Archaea;Euryarchaeota;Methanomicrobia; Methanosarcinales;:Methanosaetaceae; Methanosaeta 42.6 31.5 35.7 25.3 39.1 37.0 38.3 38.3
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Candidatus _Methanoregula; 19.7 20.5 14.7 9.5 16.2 9.0 11.5 16.3
Archaea;Euryarchaeota;Methanomicrobia;Methanosarcinales;Methanosarcinaceae;Methanosarcina; 1.2 7.0 9.7 14.4 3.3 6.8 4.0 1.6
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae;Pseudomonas; 0.5 0.7 0.9 0.6 7.7 5.6 7.4 8.7
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanolinea; 7.5 5.8 3.2 1.9 2.9 2.2 3.8 4.4
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Moraxellaceae;Acinetobacter; 0.4 2.4 3.2 6.2 1.9 2.5 2.5 0.8
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae; 0.8 2.4 3.9 4.5 1.0 3.1 2.2 0.7
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;uncultured; 1.4 0.9 0.4 0.6 3.0 1.6 1.6 2.0
Archaea;Euryarchaeota;Methanobacteria;Methanobacteriales;Methanobacteriaceae;Methanobacterium; 0.6 1.9 0.9 0.5 1.1 1.4 1.5 3.3
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Diaphorobacter; 0.3 2.5 1.6 2.0 0.2 2.4 0.8 0.2
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobacteraceae; 0.5 0.6 0.7 0.8 1.9 0.9 1.5 2.5
Archaea;Euryarchaeota;Methanomicrobia;Methanosarcinales;Methanosarcinaceae;Methanomethylovorans; 0.5 0.4 0.5 0.0 1.9 1.7 1.3 2.6
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophobacteraceae;Desulfoglaeba; 0.0 0.0 0.2 0.1 1.6 1.4 2.8 2.4
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales; 1.3 1.3 1.4 1.4 0.6 0.5 0.6 1.2
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;Leptolinea; 1.1 0.5 0.2 0.2 1.6 0.8 1.2 1.4
Bacteria;Proteobacteria;Betaproteobacteria; 0.1 0.6 1.2 1.6 0.5 1.4 0.9 0.3
Bacteria;Proteobacteria;Alphaproteobacteria;Rhizobiales;Rhizobiaceae;Rhizobium; 0.4 0.9 1.2 2.1 0.4 0.8 0.5 0.2
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Burkholderiaceae;Cupriavidus; 0.1 1.1 1.5 1.7 0.3 0.8 0.6 0.2
Archaea;Euryarchaeota;Thermoplasmata;WCHA1-57; 0.9 1.1 0.7 0.2 1.3 0.9 0.3 0.7
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Syntrophus; 2.1 1.0 0.4 0.5 0.4 0.1 0.2 1.3
210
Table 0-3 Microbial rank identified in pond 6 2011
#groupName 3.5
mbs
4
mbs
7
mbs
10
mbs
13
mbs
16
mbs
18
mbs
#totalCount 6628 7381 4941 3771 5189 5844 6830
#taxonomic term % % % % % % %
Archaea;Euryarchaeota;Methanomicrobia; Methanosarcinales;:Methanosaetaceae; Methanosaeta 18.2 18.5 21.6 27.3 16.4 14.9 8.2
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Candidatus _Methanoregula; 15.4 12.9 24.5 18.6 15.5 11.6 6.0
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Moraxellaceae;Acinetobacter; 0.8 1.2 2.8 6.5 7.7 15.6 3.5
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Syntrophus; 11.1 10.1 4.1 3.3 1.9 0.5 0.5
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanolinea; 7.1 5.7 6.2 3.6 3.4 1.8 1.1
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;uncultured; 4.9 4.8 4.4 2.9 3.2 2.8 2.8
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobacteraceae; 2.3 2.8 4.5 2.3 7.1 2.6 1.3
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Aquabacterium; 0.1 0.2 0.5 0.5 0.8 0.5 13.8
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobulbaceae;Desulfocapsa; 3.3 2.8 1.5 1.2 2.9 0.9 2.5
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;Leptolinea; 2.4 2.2 1.5 1.6 1.1 1.2 1.3
Bacteria;Spirochaetes;Spirochaetes;Spirochaetales;Spirochaetaceae;uncultured; 2.0 1.8 1.0 1.6 1.2 1.8 1.3
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae; 0.6 1.1 0.6 0.6 0.7 1.0 5.0
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae;Pseudomonas; 0.3 0.2 0.7 1.6 1.5 2.8 1.4
Bacteria;Proteobacteria;Alphaproteobacteria;Rhizobiales;Rhizobiaceae;Rhizobium; 0.2 0.2 0.5 1.1 1.8 3.3 1.0
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Delftia; 0.2 0.3 0.6 1.5 1.3 3.0 0.9
Bacteria; 0.8 0.9 0.7 1.9 1.0 1.2 1.0
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Acidovorax; 0.3 0.5 0.3 0.7 1.2 1.4 3.1
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Burkholderiaceae;Cupriavidus; 0.2 0.1 1.1 1.6 1.6 2.3 0.5
Bacteria;Bacteroidetes;Sphingobacteria;Sphingobacteriales;vadinHA17; 1.8 1.7 1.5 0.3 0.8 0.4 0.6
Bacteria;Caldiserica;Caldisericia;Caldisericales;Caldisericaceae;Caldisericum; 0.5 0.6 0.7 1.2 1.8 1.2 1.1
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Smithella; 2.2 1.9 0.6 0.3 0.3 0.4 1.2
Bacteria;Candidate_division_OP8; 0.5 0.6 0.8 1.0 1.8 1.3 0.8
211
Appendix Three: Microbial rank identified in pond 5
Table 0-4 Microbial rank identified in pond 5 2009
#groupName 2.0 2.4 4.6 6.1 7.6 9.1 10.7 12.2 13.7 15.2 19.8 25.0 29.0
mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs
#totalCount 4696 4246 4577 4092 4412 4467 4517 4258 4598 5435 3802 1469 5275
#taxonomic term % % % % % % % % % % % % %
Archaea;Euryarchaeota;Methanomicrobia;Methanosarcinales;Methanosaetaceae;Methanosaeta; 15.4 15.7 19.5 31.2 28.5 10.7 9.8 14.2 12.5 13.7 11.7 5.0 12.7
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae; 9.6 2.1 6.8 7.3 2.5 13.1 23.2 12.4 16.2 10.7 17.7 12.1 13.1
Bacteria;Proteobacteria;Betaproteobacteria; 9.7 13.4 9.2 4.1 3.3 8.9 11.4 10.8 15.4 15.1 8.8 13.7 10.1
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;uncultured; 5.8 10.1 3.4 4.2 0.9 2.7 9.3 9.7 12.8 9.0 6.7 13.0 5.1
Bacteria;Proteobacteria;Betaproteobacteria;Hydrogenophilales;Hydrogenophilaceae;Thiobacillus; 5.5 17.4 1.6 0.5 2.3 6.3 4.7 6.7 12.6 14.6 3.1 8.4 6.4
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Brachymonas; 0.8 0.5 21.3 3.5 2.4 10.0 3.5 1.1 0.4 1.8 4.2 1.2 3.6
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae; 2.8 2.2 4.7 3.5 4.3 2.5 4.5 4.8 3.7 4.9 6.0 5.0 3.1
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanolinea; 5.5 6.5 1.2 10.6 5.2 4.5 1.1 2.2 1.7 3.6 3.1 1.6 4.1
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Candidatus _Methanoregula; 12.3 11.9 1.0 3.7 6.7 0.6 0.1 1.5 0.2 0.3 2.2 2.0 2.3
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Acidovorax; 1.0 0.7 0.6 2.0 2.4 6.0 6.9 1.4 1.5 2.1 2.8 1.6 1.7
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Alcaligenaceae; 1.4 2.3 2.3 1.4 0.8 2.1 2.9 4.3 4.1 2.3 1.2 3.4 1.9
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;Thauera; 0.7 0.2 4.4 4.4 6.8 3.2 1.9 1.8 0.8 0.6 0.7 2.2 1.1
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales; 1.6 0.9 2.5 0.9 0.3 1.9 4.1 2.6 3.0 2.8 2.8 2.7 2.2
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Rhodoferax; 1.6 0.1 0.2 1.6 0.1 2.1 3.7 2.1 2.7 2.0 3.4 1.6 2.8
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae;Pseudomonas; 0.7 0.6 1.5 3.1 3.5 1.3 1.9 0.5 0.3 0.6 1.9 2.5 2.2
Bacteria;Proteobacteria;Gammaproteobacteria; 0.4 0.4 0.3 0.5 0.9 3.2 0.9 1.5 0.6 0.4 2.5 2.5 3.7
Bacteria;Proteobacteria; 0.6 0.7 0.5 1.2 0.9 0.8 1.0 1.1 1.0 0.6 2.3 2.8 2.6
Archaea;Euryarchaeota;Methanobacteria;Methanobacteriales;Methanobacteriaceae;Methanobacterium; 0.1 0.1 0.7 2.2 1.8 0.3 0.1 4.1 0.1 1.3 1.1 1.4 2.0
Bacteria;Proteobacteria;Gammaproteobacteria;Chromatiales;Chromatiaceae; 0.3 0.5 0.2 0.1 0.5 4.2 0.6 1.2 1.0 0.4 2.2 1.8 1.4
Bacteria;Proteobacteria;Betaproteobacteria;Hydrogenophilales;Hydrogenophilaceae; 0.8 2.9 0.3 0.0 0.1 0.8 0.3 0.6 1.5 1.4 0.5 1.1 0.8
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;Methyloversatilis; 0.1 0.1 0.1 0.2 0.2 1.0 0.6 2.2 0.7 1.7 1.7 1.2 1.3
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfuromonadales;Desulfuromonadaceae;Desulfuromonas; 0.5 0.1 0.4 0.5 2.6 0.6 0.2 2.5 0.8 0.6 0.2 1.2 0.6
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales; 1.8 1.4 1.0 1.0 1.4 0.4 0.1 0.4 0.2 0.2 0.3 0.1 0.6
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfuromonadales;Desulfuromonadaceae; 0.1 0.1 0.5 0.6 1.9 0.3 0.2 1.0 0.6 0.8 0.2 0.8 0.6
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;uncultured; 0.8 0.8 0.7 0.2 1.4 0.0 0.1 0.4 0.2 0.2 1.3 0.3 0.3
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanomicrobiaceae;Methanoculleus; 0.4 0.1 4.8 0.1 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Archaea;Euryarchaeota;Thermoplasmata;Thermoplasmatales;AMOS1A-4113-D04; 4.6 0.5 0.0 0.1 0.2 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0
Bacteria;Proteobacteria;Gammaproteobacteria;Legionellales;Legionellaceae;Legionella; 0.0 0.0 0.0 0.0 0.0 1.9 1.8 0.5 0.0 0.6 0.0 0.1 0.3
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Syntrophus; 1.8 0.7 0.3 0.4 1.0 0.1 0.0 0.1 0.0 0.3 0.1 0.0 0.1
Bacteria;Proteobacteria;Deltaproteobacteria;Syntrophobacterales;Syntrophaceae;Smithella; 0.8 0.4 0.5 0.2 0.5 1.2 0.0 0.0 0.1 0.3 0.2 0.2 0.3
Bacteria;Bacteroidetes;Sphingobacteria;Sphingobacteriales; 0.4 0.0 0.1 0.0 0.2 0.2 0.3 0.6 0.5 0.4 0.5 1.0 0.5
212
Table 0-5 Microbial rank identified in pond 5 2010
#groupName 3 6 9 12 15 18 21 27 33 39 45 51
mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs mbs
#totalCount 5504 2667 6412 2787 9845 7710 8825 8156 5291 8657 7638 5889
#taxonomic term % % % % % % % % % % % %
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae;Pseudomonas; 24.7 56.5 26.0 51.8 61.3 16.7 25.7 32.7 20.1 40.7 42.5 21.0
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Acidovorax; 3.1 2.9 4.3 6.3 7.0 11.3 23.1 3.5 3.6 5.8 10.7 48.5
Archaea;Euryarchaeota;Methanomicrobia;Methanosarcinales;Methanosaetaceae;Methanosaeta; 17.0 6.4 9.8 4.3 2.4 29.9 0.4 1.3 9.5 2.2 1.1 0.4
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae; 1.5 3.1 2.0 3.1 2.0 9.4 12.8 2.3 4.2 3.5 2.3 13.7
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Moraxellaceae;Acinetobacter; 0.5 2.6 0.7 1.5 1.1 0.7 0.3 14.1 21.3 3.5 7.9 0.6
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfuromonadales;Desulfuromonadaceae;Desulfuromonas; 1.3 2.1 0.7 1.3 2.1 2.2 2.9 9.8 6.2 8.7 5.4 0.9
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfuromonadales;Desulfuromonadaceae; 0.3 1.4 1.0 1.2 1.1 0.8 0.9 11.4 1.9 7.0 4.4 0.4
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Comamonas; 0.5 0.6 0.4 1.4 1.6 1.4 4.2 2.6 0.9 5.1 5.0 1.0
Bacteria;Proteobacteria;Betaproteobacteria;Rhodocyclales;Rhodocyclaceae;Thauera; 2.5 1.8 2.6 3.3 4.1 0.9 4.6 0.9 0.6 1.0 1.0 0.2
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Methanolinea; 1.9 1.1 1.9 1.1 1.4 5.0 0.3 0.6 8.0 1.0 0.4 0.1
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;uncultured; 7.1 4.1 2.7 2.1 1.2 0.2 1.0 1.4 0.9 0.8 0.8 0.2
Archaea;Euryarchaeota;Methanomicrobia;Methanomicrobiales;Candidatus _Methanoregula; 3.9 0.8 5.4 2.0 0.2 0.3 0.2 0.3 2.5 0.2 0.4 0.1
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Hydrogenophaga; 1.1 4.4 1.6 0.3 0.4 0.1 4.3 0.3 0.5 0.3 0.6 0.2
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfovibrionales;Desulfomicrobiaceae;Desulfomicrobium; 0.1 0.8 2.1 1.0 1.2 0.1 0.1 1.7 0.5 3.7 1.2 0.2
Bacteria;Firmicutes;Clostridia;Clostridiales;Peptococcaceae; 1.2 0.5 3.0 1.4 1.5 0.8 0.0 0.8 0.3 1.8 0.4 0.1
Bacteria;Firmicutes;Bacilli;Lactobacillales;Streptococcaceae;Streptococcus; 1.1 0.0 7.2 2.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0
Bacteria;Proteobacteria;Betaproteobacteria;Hydrogenophilales;Hydrogenophilaceae;Thiobacillus; 0.5 0.3 1.0 0.7 1.1 0.6 1.3 0.4 0.2 0.2 1.6 1.5
Bacteria;Chloroflexi;Anaerolineae;Anaerolineales;Anaerolineaceae;Leptolinea; 4.7 0.6 1.2 0.6 0.3 0.1 0.3 0.3 0.4 0.4 0.4 0.0
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Rhodoferax; 0.5 0.4 0.5 0.8 0.4 0.1 2.6 0.8 0.5 1.3 0.8 0.2
Bacteria;Proteobacteria;Gammaproteobacteria;Pseudomonadales;Pseudomonadaceae; 0.8 1.0 1.0 1.0 0.3 0.7 0.2 0.3 1.4 0.2 0.3 1.0
Bacteria;Proteobacteria;Betaproteobacteria;Burkholderiales;Comamonadaceae;Aquamonas; 0.1 1.1 0.3 0.4 1.0 0.7 1.8 0.2 0.3 0.5 0.6 0.1
Bacteria;Proteobacteria;Deltaproteobacteria;Desulfobacterales;Desulfobulbaceae;Desulfocapsa; 1.7 0.2 1.1 0.4 0.4 0.3 0.3 0.2 0.5 1.2 0.6 0.0
Bacteria;Proteobacteria;Gammaproteobacteria; 0.1 0.2 0.0 0.3 0.1 0.9 0.1 0.2 3.3 0.0 0.2 1.0
Bacteria;Firmicutes;Clostridia;Clostridiales;Eubacteriaceae;Acetobacterium; 0.0 0.0 0.0 0.0 0.0 0.1 0.0 5.9 0.0 0.1 0.1 0.0
213
Appendix Four: Naphthenic acid isolates DNA sequences
ER10 Complete sequence: Acidovorax sp. strain ER10 (99 % max identity, query length 1307)
CTTACNCNTGCAAGTCGAACGGTAACAGGTCTTCGGATGCTGACGAGTGGCGAACGGGTGAGTAATACATCGGAACGTG
CCCGATCGTGGGGGATAACGGAGCGAAAGCTTTGCTAATACCGCATACGATCTACGGATGAAAGCAGGGGACCGCAAGG
CCTTGCGCGGACGGAGCGGCCGATGGCAGATTAGGTAGTTGGTGGGATAAAAGCTTACCAAGCCGACGATCTGTAGCTGGTCTGAGAGGACGACCAGCCACACTGGGACTGAGACACGGCCCAGACTCCTACGGGAGGCAGCAGTGGGGAATTTTGGA
CAATGGGCGAAAGCCTGATCCAGCCATGCCGCGTGCAGGATGAAGGCCTTCGGGTTGTAAACTGCTTTTGTACGGAACGA
AAAGACTTCTTCTAATACAGGAGGTCCATGACGGTACCGTAAGAATAAGCACCGGCTAACTACGTGCCAGCAGCCGCGGTAATACGTAGGGTGCAAGCGTTAATCGGAATTACTGGGCGTAAAGCGTGCGCAGGCGGTTATATAAGACAGATGTGAAAT
CCCCGGGCTCAACCTGGGAACTGCATTTGTGACTGTATAGCTAGAGTACGGTAGAGGGGGATGGAATTCCGCGTGTAGCA
GTGAAATGCGTAGATATGCGGAGGAACACCGATGGCGAAGGCAATCCCCTGGACCTGTACTGACGCTCATGCACGAAAGCGTGGGGAGCAAACAGGATTAGATACCCTGGTAGTCCACGCCCTAAACGATGTCAACTGGTTGTTGGGTCTTCACTGACT
CAGTAACGAAGCTAACGCGTGAAGTTGACCGCCTGGGGAGTACGGCCGCAAGGTTGAAACTCAAAGGAATTGACGGGGA
CCCGCACAAGCGGTGGATGATGTGGTTTAATTCGATGCAACGCGAAAAACCTTACCCACCTTTGACATGTACGGAATCCTTTAGAGATAGAGGAGTGCTCGAAAGAGAGCCGTAACACAGGTGCTGCATGGCTGTCGTCAGCTCGTGTCGTGAGATGTTG
GGTTAAGTCCCGCAACGAGCGCAACCCTTGTCATTAGTTGCTACATTTAGTTGGGCACTCTAATGAGACTGCCGGTGACA
AACCGGAGGAAGGTGGGGATGACGTCAAGTCCTCATGGCCCTTATAGGTGGGGCTACACACGTCATACAATGGCTGGTACAGAGGGTTGCCAACCCGCGAGGGGGAGCCAATCCCATAAAGCCAGTCGTAGTCCGGATCGCAGTCTGCAACTCGACTG
CGTGAAGTCGGAATCGCTAGTAATCGCGGATCAGAA
ER19 Complete sequence: Xanthobacter sp. strain ER19 (99 % max identity, query length 1249)
CATGCAGTCGAGCGCCCAGCAATGGGAGCGGCAGACGGGTGAGTAACGCGTGGGGATCTGCCCGATGGTACGGAATAAT
TCCGGGAAACTGGGACTAATACCGTATGTGCCCGCAAGGGGAAAGATTTATCGCCATCGGATGAACCCGCGTCGGATTAGCTAGTTGGTGTGGTAAAGGCGCACCAAGGCGACGATCCGTAGCTGGTCTGAGAGGATGATCAGCCACACTGGGACTGAG
ACACGGCCCAGACTCCTACGGGAGGCAGCAGTGGGGAATATTGGACAATGGGCGCAAGCCTGATCCAGCCATGCCGCGT
GAGTGATGAAGGCCTTAGGGTTGTAAAGCTCTTTCGCCGGTGAAGATAATGACGGTAACCGGAGAAGAAGCCCCGGCTA
ACTTCGTGCCAGCAGCCGCGGTAATACGAAGGGGGCAAGCGTTGCTCGGAATCACTGGGCGTAAAGCGCACGTAGGCGG
GTCGTTAAGTCAGAGGTGAAAGCCTGGAGCTCAACTCCAGAACTGCCTTTGATACTGGCGACCTAGAGTTCGAGAGAGGT
TGGTGGAACTGCGAGTGTAGAGGTGAAATTCGTAGATATTCGCAAGAACACCAGTGGCGAAGGCGGCCAACTGGCTCGATACTGACGCTGAGGTGCGAAAGCGTGGGGAGCAAACAGGATTAGATACCCTGGTAGTCCACGCCGTAAACGATGGATGC
TAGCCGTTGGGGAGCTTGCTCTTCAGTGGCGCAGCTAACGCTTTAAGCATCCCGCCTGGGGAGTACGGTCGCAAGATTAA
AACTCAAAGGAATTGACGGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGAAGCAACGCGCAGAACCTTACCAGCCTTTGACATGGCAGGGCGATTTCCAGAGATGGATCTCTCTCAGCAATGAGCCTGCACACAGGTGCTGCATGGCTGTCG
TCAGCTCGTGTCGTGAGATGTTGGGTTAAGTCCCGCAACGAGCGCAACCCTCGCCCCTAGTTGCCATCATTCAGTTGGGCA
CTCTAGGGGGACTGCCGGTGATAAGCCGCGAGGAAGGTGGGGATGACGTCAAGTCCTCATGGCCCTTACGGGCTGGGCTACACACGTGCTACAATGGTGGTGACAGTGGGATGCGAAAGGGCGACCTCTAGCAAATCTCCAAAAGCCATCTCAGTTCG
GATTGCACTCTGCAACTCGAGTGCATGAAGTTGGAATCGCTAGTAATCGNGGATCAGC
ER28 Complete sequence: Pseudomonas putida strain ER28 (100 % max identity, query length 1302)
TGCAGTCGAGCGGATGACGGGAGCTTGCTCCTTGATTCAGCGGCGGACGGGTGAGTAATGCCTAGGAATCTGCCTGGTAG
TGGGGGACAACGTTTCGAAAGGAACGCTAATACCGCATACGTCCTACGGGAGAAAGCAGGGGACCTTCGGGCCTTGCGC
TATCAGATGAGCCTAGGTCGGATTAGCTAGTTGGTGGGGTAATGGCTCACCAAGGCGACGATCCGTAACTGGTCTGAGAG
GATGATCAGTCACACTGGAACTGAGACACGGTCCAGACTCCTACGGGAGGCAGCAGTGGGGAATATTGGACAATGGGCG
AAAGCCTGATCCAGCCATGCCGCGTGTGTGAAGAAGGTCTTCGGATTGTAAAGCACTTTAAGTTGGGAGGAAGGGCAGTAAGTTAATACCTTGCTGTTTTGACGTTACCGACAGAATAAGCACCGGCTAACTCTGTGCCAGCAGCCGCGGTAATACAGA
GGGTGCAAGCGTTAATCGGAATTACTGGGCGTAAAGCGCGCGTAGGTGGTTTGTTAAGTTGGATGTGAAAGCCCCG
GGCTCAACCTGGGAACTGCATCCAAAACTGGCAAGCTAGAGTACGGTAGAGGGTGGTGGAATTTCCTGTGT
AGCGGTGAAATGCGTAGATATAGGAAGGAACACCAGTGGCGAAGGCGACCACCTGGACTGATACTGACACTGAGGTGCGAAAGCGTGGGGAGCAAACAGGATTAGATACCCTGGTAGTCCACGCCGTAAACGATGTCAACTAGCCGTTGGAATCCTTG
AGATTTTAGTGGCGCAGCTAACGCATTAAGTTGACCGCCTGGGGAGTACGGCCGCAAGGTTAAAACTCAAATGAATTGAC
GGGGGCCCGCACAAGCGGTGGAGCATGTGGTTTAATTCGAAGCAACGCGAAGAACCTTACCAGGCCTTGACATGCAGAGAACTTTCCAGAGATGGATTGGTGCCTTCGGGAACTCTGACACAGGTGCTGCATGGCTGTCGTCAGCTCGTGTCGTGAGAT
GTTGGGTTAAGTCCCGTAACGAGCGCAACCCTTGTCCTTAGTTACCAGCACGTAATGGTGGGCACTCTAAGGAGACTGCC
GGTGACAAACCGGAGGAAGGTGGGGATGACGTCAAGTCATCATGGCCCTTACGGCCTGGGCTACACACGTGCTACAATGGTCGGTACAGAGGGTTGCCAAGCCGCGAGGTGGAGCTAATCTCACAAAACCGATCGTAGTCCGGATCGCAGTCTGCAACT
CGACTGCGTGAAGTCGGAATCGCTAGTAATCGCGAATCATAA
214
Appendix Five: Diversity indexes for pond 6
Table 0-6 Taxonomic classification and estimated richness for pond 6 samples using
95% similarity values
sample # of reads # of OTUs Chao
index
Shannon
index
Simpson
index
Pond 6 2008 3.0 mbs 11350 1349 2801.7 5.78 0.01
Pond 6 2008 5.0 mbs 10612 1355 3122.5 5.63 0.02
Pond 6 2008 6.0 mbs 9860 1091 2454.8 5.42 0.02
Pond 6 2008 8.0 mbs 10824 1259 3027.2 5.27 0.03
Pond 6 2008 9.0 mbs 10273 1171 2759.5 5.53 0.02
Pond 6 2008 2.0 mbs 5222 888 2531.9 4.98 0.06
Pond 6 2008 11.0 mbs 6977 937 2141.7 5.81 0.01
Pond 6 2008 12.0 mbs 9511 1135 2543.3 5.84 0.01
Pond 6 2008 14.0 mbs 7637 909 2137.9 5.57 0.02
Pond 6 2008 15.0 mbs 9826 1165 2619.1 5.91 0.01
Pond 6 2008 17.0 mbs 9818 1064 2667.3 5.56 0.01
Pond 6 2008 18.0 mbs 9283 1061 2311.0 5.70 0.01
Pond 6 2010 3.0 mbs 12853 1640 4195.2 5.17 0.05
Pond 6 2010 6.0 mbs 8964 1302 3396.5 5.24 0.04
Pond 6 2010 9.0 mbs 10570 1537 3742.0 5.33 0.04
Pond 6 2010 12.0 mbs 10029 1463 3739.7 5.47 0.03
Pond 6 2010 15.0 mbs 11434 1499 3798.9 5.11 0.05
Pond 6 2010 18.0 mbs 9698 1481 3843.6 5.38 0.04
Pond 6 2010 21.0 mbs 12180 1757 4823.5 5.38 0.05
Pond 6 2010 22.0 mbs 11773 1587 3975.4 5.20 0.05
Pond 6 2011 3.5 mbs 10033 1452 3274.5 5.68 0.02
Pond 6 2011 4.0 mbs 11180 1645 3502.2 5.85 0.02
Pond 6 2011 7.0 mbs 7679 1109 2239.9 5.30 0.03
Pond 6 2011 10.0 mbs 5813 911 1905.9 5.21 0.03
Pond 6 2011 13.0 mbs 7951 1143 2409.6 5.58 0.02
Pond 6 2011 16.0 mbs 9687 1254 2797.3 5.56 0.02
Pond 6 2011 18.5 mbs 9838 1435 2915.2 5.87 0.01
215
Appendix Six: Rarefaction curve of all pond 6 samples
Figure 0-1 Rarefaction curves for the microbial community of Suncor pond 6 in the
years (A) 2008, (B) 2010, and (C) 2011.
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 2000 4000 6000 8000
# of
OT
Us
# of reads
Pond 6 2010 6 mbs
Pond 6 2010 9 mbs
Pond 6 2010 12 mbs
Pond 6 2010 15 mbs
Pond 6 2010 18 mbs
Pond 6 2010 21 mbs
Pond 6 2010 22 mbs
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000
# of
OT
Us
# of reads
Pond 6 2008 2 mbs
Pond 6 2008 3 mbs
Pond 6 2008 5 mbs
Pond 6 2008 6 mbs
Pond 6 2008 8 mbs
Pond 6 2008 9 mbs
Pond 6 2008 11 mbs
Pond 6 2008 12 mbs
Pond 6 2008 14 mbs
Pond 6 2008 15 mbs
Pond 6 2008 18 mbs
Pond 6 2008 21 mbs
0
200
400
600
800
1000
1200
1400
1600
1800
0 1000 2000 3000 4000 5000 6000 7000 8000
# of
OT
Us
# of reads
Pond 6 2011 3.5 mbs
Pond 6 2011 4 mbs
Pond 6 2011 7 mbs
Pond 6 2011 10 mbs
Pond 6 2011 13 mbs
Pond 6 2011 16 mbs
Pond 6 2011 18.5 mbs
A
B
C
216
Appendix Seven: Diversity indexes for pond 5
Table 0-7 Taxonomic classification and estimated richness for pond 5 samples using
95% similarity values.
Sample # of
reads
# of
OTUs
chao
index
shannon
index
simpson
index
Pond 5 2009 1.8 mbs 4697 2059 6934.6 6.63 0.01
Pond 5 2009 2.4 mbs 4246 1514 4470.3 6.04 0.01
Pond 5 2009 4.6 mbs 4583 1868 6323.8 6.55 0.01
Pond 5 2009 6 mbs 4094 1845 6934.7 6.56 0.01
Pond 5 2009 8 mbs 4418 1850 6515.6 6.51 0.01
Pond 5 2009 9 mbs 4474 1925 5602.0 6.57 0.01
Pond 5 2009 11 mbs 4520 1953 5798.4 6.61 0.01
Pond 5 2009 12 mbs 4258 1825 5681.8 6.52 0.01
Pond 5 2009 14 mbs 4599 1616 4418.5 6.20 0.01
Pond 5 2009 15 mbs 5436 2239 7377.6 6.63 0.01
Pond 5 2009 20 mbs 3804 1989 7871.0 6.86 0.00
Pond 5 2009 25 mbs 1472 832 3476.2 6.13 0.01
Pond 5 2009 29 mbs 5276 2523 8660.1 6.98 0.00
Pond 5 2010 3 mbs 5507 1136 2494.0 5.69 0.01
Pond 5 2010 6 mbs 2669 562 1260.0 4.81 0.03
Pond 5 2010 9 mbs 6432 1571 4455.7 5.90 0.01
Pond 5 2010 12 mbs 2789 699 1796.5 5.07 0.02
Pond 5 2010 15 mbs 9845 883 2098.7 3.81 0.12
Pond 5 2010 18 mbs 7711 2459 7237.1 6.33 0.01
Pond 5 2010 21 mbs 8825 1123 2277.1 4.48 0.05
Pond 5 2010 27 mbs 8156 791 1721.1 4.10 0.06
Pond 5 2010 33 mbs 5293 1854 5919.0 6.22 0.01
Pond 5 2010 39 mbs 8658 690 1664.6 3.87 0.07
Pond 5 2010 45 mbs 7638 904 2266.8 4.33 0.06
Pond 5 2010 51 mbs 5889 1480 4274.6 4.81 0.10
217
Appendix Eight: Rarefaction curve pond 5.
Figure 0-2 Rarefaction curves for the microbial community of Suncor pond 5 in the
years (A) 2009, (B) 2010.
0
500
1000
1500
2000
2500
3000
0 2000 4000 6000 8000 10000 12000
# o
f O
TU
s)
# of reads
Pond 5 2010 3 mbs
Pond 5 2010 6 mbs
Pond 5 2010 9 mbs
Pond 5 2010 12 mbs
Pond 5 2010 15 mbs
Pond 5 2010 18 mbs
Pond 5 2010 21 mbs
Pond 5 2010 27 mbs
Pond 5 2010 39 mbs
Pond 5 2010 45 mbs
Pond 5 2010 51 mbs
Pond 5 2010 33 mbs
0
500
1000
1500
2000
2500
3000
0 1000 2000 3000 4000 5000 6000
# o
f O
TU
s
# of reads
Pond 5 2009 1.8 mbs
Pond 5 2009 2.4 mbs
Pond 5 2009 4.6 mbs
Pond 5 2009 6.1 mbs
Pond 5 2009 7.6 mbs
Pond 5 2009 9.1 mbs
Pond 5 2009 10.7 mbs
Pond 5 2009 12 mbs
Pond 5 2009 14 mbs
Pond 5 2009 15 mbs
Pond 5 2009 20 mbs
Pond 5 2009 25 mbs
A
B
218
Appendix Nine: Diversity indexes for surface water samples
Table 0-8 Taxonomic classification, observed and estimated richness for TPW
samples using 95% similarity values.
group # of reads # of OTUs Chao
index
Shannon
index
Simpson
index
P6 2008 10009 311 409.4 3.87 0.06
P5 2009 2827 278 439.6 4.33 0.03
P6 2011 6342 373 565.4 4.13 0.05
219
Appendix Ten: Rarefaction curves for surface water samples
Figure 0-3 Rarefaction curves for the microbial community in TPW.
0
50
100
150
200
250
300
350
400
0 5000 10000 15000
# o
f O
TU
s
# of reads
P6 2008
P5 2009
P5 2011
220
Appendix Eleven: Sulfur metabolism in tailings from pond 6 2008 and 2010.
Obtained from metagenomic analysis by KEGG (http://www.genome.jp/kegg/)
Figure 0-4 Sulfur metabolism in tailings ponds obtained by metagenomics.
221
Appendix Twelve: Iron concentration in oil sands tailings ponds
Figure 0-5 Iron concentration (Fe (II)) determined by the Ferrozine assay 213
in oil
sands tailings. (A) pond 6 sampled in 2011, and (B) pond 6 sampled in 2012.
0
5
10
15
20
0 2 4 6 8 10D
epth
(m
bs)
Iron concentration (mM)
0
5
10
15
20
0 10 20 30 40 50
Dep
th (
mb
s)
Iron concentration (mM)
A
B
